I was wondering just what the difficulty is with having multiple users on the Prime? In regard to Gmail, I have 3 different accounts connected with my app and can toggle notifications, what to sync (down to the label within ea. account) on & off. In any contacts situation I've always been asked what account to sync with and it has worked seemlessly.
In my ICS+ Browser, when I go to Google+ or Amazon there's no problem signing into accounts & I'm a heavy user of my Prime for that kind of thing. When adding or perusing bookmarks they're associated with each gmail account (the app organizes it that way & asks every time you tweak or set up) so that's not an issue.
As far as apps like Picasa Tool, I've never had a problem with Google+ albums & such. I can't think of an instance with a paid app, but I would think if the app doesn't support multiple users you're going to have to pay twice for it anyway most of the time, right?
If it's privacy you're concerned about, the ability to keep secrets easily is a different matter entirely.
I'm just sayin', I haven't had any problems with multiple accounts on my Prime. No one asked you about this postulation & I don't want to see my Prime blamed unfairly - I love it! :~)