Get a simple gmail account and join up, you can switch accounts fairly easily (although it sucks when you have an apps and separate account and constantly have to log in and out)
That's what I'm doing atm (just to test it out), but it's really annoying since all other Google services use my apps account. So I'd have to login/logout constantly if I wanted to use G+ throughout the day. Not worth it.
Anyway, I'm sure they'll extend support to apps users eventually.