Migration assistance does not handle the iPhoto library well sometimes - the best way is to drag the bad iphoto library from the pictures folder on the new system to the desktop, connect the two systems together (network, firewire target mode, etc) and drag the iPhoto library intact as a single entity from the old system to the pictures folder of the new system and launch iPhoto on the new system - it will open and convert the iPhoto library as necessary and you will be fine - once you test the iPhoto library you can delete the one on the desktop
If you have iPhoto 9.3 or later you can open an Apertrure 3.3 or later library directly -
Actually the reply from Larry HN, the literature he cited, and other literature I found along the way (including advice from my son who is in art school), led me to the best solution for me: Junk the libraries and import photos in the more conventional way into the Pictures folder in Finder. There is some discussion about difficulties with seeing connected cameras as devices, etc., but the Apple Image Capture application works fine for me. It always "sees" my connected camera, and is simple. You can also make Adobe Bridge work for this but I like the simpler Image Capture. I like working with photos with Adobe Photoshop, and it's just easier for me (personal preference) to work with photos with Photoshop interacting directly ("open" etc.) with good, old-fashioned files in the Finder.
One caution: if you are importing Raw or similar formats (or dual formats) from your camera (whether you are using Image Capture, Adobe Bridge, Aperture, or iPhoto), watch those import settings. I discovered that I had previously imported a number of photos from my camera, where the camera was capturing combined Fine and Raw image files, but due to oversimplified default user settings, I never imported anything but the JPEGs.
If you have been using Aperture or iPhoto and have photos segregated by "projects" or "events" or whatever, you can export them to your Pictures folder and the export utility will create sub-folders for each project or event, thereby preserving your organization. Again, just watch those export settings to make sure all your images go over, not just JPEGs.
Per earlier discussion, it did prove true that if you follow the instructions your Aperture Library and your iPhoto Library will be one and the same. It is wonderful that Apple give us so many good fits for personal preferences. It is just easier, more straightforward, and more logical for me to work directly between the app I use for editing (Photoshop) and the image files, stored in the old-fashioned simple way (RAW, JPEG, or whatever, files in a Finder folder), and not have a "database" file approach like Aperture or iPhoto in the middle. If I take a bunch of photos at a particular event, say my son's upcoming graduation, It's a very familiar process for me to create a sub-folder in that Finder Pictures folder and name it "son's graduation" or whatever.
One neat thing about these user community support forums is that a reply from just one person, especially with links to literature, can lead you to very complete and dependable answers.