Well, I'm new to +1. This will be easier when I can use Profiles with my Google Apps for Business!
one plus one
Ari Malek: G+ is actively preventing "business" entities from joining at this point. It's only for confirmed "individuals." Business profiles will supposedly roll out later this year. So, just guessing, Google Apps logins are presumed guilty as they're typically associated with businesses. Not sure, but it makes sense to me :-)
Gary Levine: I did submit an inquiry to Google, and they confirmed what Ari says about the future support. Not sure I grasp why businesses are "guilty" but, I have also discovered Tracy's response is also true: I use my personal profile (email@example.com), and can just go to another window to view/work on G+ (or Groups).
Maryn - to do that, you have to go to your user account settings, and turn "Multiple Sign-on" to "on." If you search "multiple sign on" in Google, you should be able to find better directions than I could give. But I think they ran this this whole accounts/profiles stuff through the "department of confusion and obfuscation department" before releasing it.