Greetings Everyone. I have posted to this thread several times, and followed all the replies. I believe that we have jointly figured out all that is happening with this iPhoto to Photos update but just haven't put all of the pieces together. Here is my best guess as to what is happening (in at least in a lot of cases).
1. We downloaded OS 10.10.3 which included the new Photos software to our computer. Most of us followed the directions from Apple and downloaded all the newest software for the iPhone and iPad. If you have a number of devices, you may had multiple iPhones, iPads, other desktop and laptop computers. In other words, lots and lots of devices. We then followed the directions from Apple for connecting to iCloud. It looks like the "process" starts, but then "jams up" and stops. This may, or may not, be the case. You can observe the uploading of photos to iCloud by logging into your iCloud account > Photos > Moments and scrolling down to the bottom of that page. There will be a count of the number of photographs and videos that has been uploaded. There will be the spinning timer with the word "Updating." Eventually the timer will stop and the number of photos/videos will increase. This spinning timer can take anywhere from a few seconds to several minutes, depending on how many photos/videos have been uploaded. At 30K photos it routinely takes my computer 2-3 minutes count the total number of photographs. You can start the updating count again by mouse clicking on the browser's refresh button. By noting the number change this is one way you can tell if uploading is really occurring.
2. In the past, when we have downloaded software, we're used to having it work right after we have it installed. This has NOT been my experience with Photos. First, I have FIOS with 75Mbps upload and download speed, but was only averaging 1Mbps during the uploading. I also had to upgrade my iCloud storage from 20 GB to 200GB because I was around 135 GB "short" of needed storage space. The good news is that this is another indication that something is happening. The bad news is that this is a glacial upload speed. One of the writers in this thread mentioned that Apple told him their servers are overwhelmed and to wait a few weeks before uploading to iCloud so they can bring more servers online. It stands to reason that if I'm uploading 135GB of photos/videos, and you are uploading GB's of media, and so are tens of thousands of other users, then there will be a lot of lag (apparently Apple did not anticipate this high initial usage).
3. How fast your photos upload will depend on a lot of factors -- the processing speed of your computer, the speed of your Internet, how stable your Internet connection is, how long you leave Photos running, etc. Another hint, in System Preferences > Energy Saver set "Computer Sleep" to NEVER. That way you let the uploading continue over long periods of time without your computer automatically going to sleep. It took me around 70 hours of run time before all 30K photos were uploaded. You can start and stop Photos during this process, I restarted my computer several times.
4. As iCloud was slowly filling with photographs, the photos started to appear on my iPhone (another hint that the process is working). HINT: If you have a lot of photos you may not want iCloud to send them all to your iPhone as they take up a lot of memory. You can tell you iPhone to store what I'm guessing are the thumbnails, rather than the full resolution photos. I have an iPhone 6 with 128 GB and 30K photos required more memory that was available on my iPhone using full resolution. Even the smaller versions of pictures took up over 50 GB.
5. I have also noticed that other software interferes with the sending/receiving of photos to iCloud and/or the processing of the Photos program. Mail, for example, when it runs it periodically checks to see if you have new mail stored on your companies server(s). I have Gmail accounts, a Verizon account, a Yahoo account, etc. Mail will attempt to make connections over the Internet with the mail servers. This in turn interrupts the transfer of data to iCloud. I have had to Force Quit Mail because of failed connections, and Mail just freezes up. I also noticed that my external Time Machine hard drive, if it is doing an update, will slow down the data transfer. The computer needs processing power and data transfer to update Time Machine, and apparently can't access that, update Photos and iCloud simultaneously (or at the very least, slows down ALL processes).
6. SUMMARY SO FAR. Photos has to take and process your iPhoto pictures/videos (chewing up computer processing speed), then upload them to iCloud. iCloud then takes them and downloads them to your other connected devices. So, one batch of photos UP to iCloud, then iCloud turns around and SENDS them back to ALL your connected devices. I have 4 devices in my home. Multiply that times tens of thousands of new Photo users, times the number of devices each household has ... you can see why iCloud seems to be crawling right now. I have also continued to take new photographs, thus uploading even more photos to iCloud, then iCloud has to download them to my other devices.
7. While all this is happening, I also noticed that many of Photos features (like editing) simply did not work, that "events" and "albums" were not being carried over, etc. In the beginning of the process, only 2 or 3 of the editing features worked. As time went on, more and more of these features became active. After about a week, all of the editing functions then worked. After almost 2 weeks, the facial recognition part of Photos became active. At first just the photos of faces recognized from iPhoto were there, but I could not access them nor do any additional faces. Then a day later (after leaving the computer running another continuous 12 hours), I could utilize the full features of facial recognition.
8. It seems to me that the Photos software doesn't totally work until more and more of your photographs are uploaded. My guess is that the program is busy converting media from iPhoto to Photo, then busy uploading all the media (plus it's associated data) to iCloud. It also had to tell iCloud the albums individual photos were in, etc. I'm guessing that the software developers delayed the implementation of Photos editing, etc. until the full resolution photos were uploaded to iCloud. I suppose it might get confusing for the software if, during the initial upload to iCloud, one started to edit photographs.
OVERALL SUMMARY: Moving from iPhoto to Photos is a complex, multi-step process that takes a LOT of time to complete. The process utilizes a lot of computational power as well as a lot of Internet bandwidth. Besides a few exceptions mentioned in #1, there is frustratingly little information given to the end-user as to the progress of your update, or how long it needs to complete the process. Apple probably left out the "time" indicator because a lot depends on your internet speed, but they should have at least had a drop-down with a check off box section, telling you the steps it is working on, steps completed, and steps left to do. The software needs SOMETHING to let you know that "stuff" is happening. Unfortunately, the best you can do is take some notes on how many photos are uploaded, what parts of Photo is working, and what's not working. Then check your notes from time to time to see if progress is being made. DON'T let your computer automatically go into SLEEP mode. Let it run continuously (and without other software running) for as long as you can. It is okay to shut down Photos / iCloud. I did it many times so I could get mail and do other things. At the very least I let it run continuously over night.
I can say that after 2 weeks and around 100 hours of connections to iCloud and letting Photos run -- that everything appears to be working, and working as it should. Still, when I first start Photos, there is still a noticeable lag (minutes) as Photos connects with iCloud to upload any new photos I have added to my desktop computer and iCloud then sends to my iPhone, plus upload any photos from my iPhone and send them to my desktop AND any edited photos - basically "housekeeping" to make sure all the devices and the iCloud are kept up-to-date. All this takes some computational time and Internet time. If I start the computer, Photos and Mail all around the same time, Mail still lags and occasionally crashes. It's even worse if Time Machine decides it's time for an update. I must have sent in 10-15 Mail "crash reports" to Apple, I'm hoping it's a problem that has a software fix or will work itself out once iCloud access speed increases.
I also realize that this isn't going to solve everyone's issues that have written in this thread. I don't have any additional software connected to iPhoto/Photos. I'm unsure what effect Lightroom might have, or any plugins? I do have Photoshop Elements 13, and did activate Organizer before switching to Photos, just to make one more backup of all my photos (the other on Time Machine). Overkill, but I really didn't want to lose 30k photos.