It seems we were led to believe the change over from MobileMe would be simple and easy but this forum has given us a preview of a number of nightmare scenarios awating some poor souls. I am going to wait at least 6 months before considering iCloud conversion and hopefully someone can create a roadmap for us all to follow depending on the individual's combination of Apple, Mail, and iTunes IDs.
I have collected various comments regarding the .mac and .me addresses and IDs which I believe I now understand. I am passing them on to you in case it can be of some help. Sorry I couldn't answer your main questions.
iCloud with .mac and .me
Apple has stated that both mac.com as well as me.com addresses will continue to work for both your Apple id and your email address.You may have a temporary issue (?) but your Mac.com address will be fine.
Some Apple IDs, like those ending in @mac.com or @me.com, can't be changed.
If you've used the same @me.com or @mac.com AppleID for iTunes as well as MobileMe, then it should all be a single iCloud/iTunes account.
Only AppleID's that end in @me.com or @mac.com can be moved to iCloud. If you enter any other AppleID you are creating a new iCloud account with a new @me.com email address.
@mac.com and @me.com are the same internally to Apple. Your @mac.com existed before @me.com, so the @me.com is an alias of @mac.com. The latter is your REAL email address.
You have a me.com account (which is linked to my mac.com account), you can sign in to iCloud using either one of the accounts.
Definitely helpful. Though, I was wondering about what I would do in this case...
I have a:
Mac ID - Use it for mail, syncing - basically everything mac-related. (iphone, etc.)
I use my wife's Apple ID on our computer as my way to download music.
I've always used the separate email address for my itunes purchases. So, I don't know if that is my "apple ID" or if my email address (my mail @me.com) is my apple ID. I'm assuming I'd log onto the cloud using my email. But, what about backing up all the music, etc? Purchases?
No use complaining about all of this, as it's unstoppable. But, this is as upset I've been with Apple... maybe ever. This seems so patently illigocial, I can't get my head around it.
I never had a Mobile Me account. However, putting myself in that hypothetical situation; I would do the following about those three missing things:
iDisk: There are plenty of free file hosting services out there. Also, in a way, Documents and Data sync can act as a replacement; especially if you do this: http://9to5mac.com/2011/11/03/apple-working-on-dropbox-like-icloud-file-sync/ . 5Gb is plenty for me, even using this little trick. It's too bad though you have to pay for the same amount of space in iCloud that you used to get for free (before MobileMe) back in the days of .Mac and even iTools (eesh, showing my Mac age here). I don't do large files over the net though, because the high-speed in my area is not reliable enough.
Gallery: Again, there are a fair amount of decent browser-based photo sharing services out there. I use Flickr because I can play with the feed and automatically embed whatever I upload there into my website (I use that to create a grid of photos as a background). Good stuff; and once you get your embed code right, you'll never have to touch it again (really I didn't even type out any code, just used some jQuery copy and paste). I find that I use my device to share photos most of the time though, so Photostream actually works. Anything else can be looked at at my Flickr channel.
iWeb: This one stings. All the free website hosting services out there are quite horrible (the only decent one is Wix, but they only allow creation of Flash websites, nasty!). A lot of cheap replacements also cap your bandwidth. The best bargain for unlimited bandwidth I found was GoDaddy's middle-tier plan at $10/month at the highest. The cool thing is though they throw 150 gigs of space at you for that price. If you're willing to play with FTP, you can actually use that as an iDisk replacement too, just make sure to mark anything you don't want going over the web for absolutely no sharing.
As for the two logins issue; I would use Mac ID for staying in sync and your wife's for purchases. Keeping things that way is the simplest route, as your iPhone will remember that it should use your wife's for purchases and your Mac ID for iCloud (since you put one in at the iTunes and App stores and another in the iCloud section in the Settings app.
I came across this link which discusses different scenarios regarding IDs and Passwords for the various iCloud components. http://forums.macrumors.com/showthread.php?t=1248112
I hope it offers you a solution.