Not that you care about me, particularly, but the stories/anecdotes going around describing complete account blocking (1) have kept me from accepting the invitation I received.
Google's help pages, which I'd started reading through, make it sound as if the Google+ profile exists separate from this other access. But I've now seen enough such "WTF I'm blocked -- from everything!" stories to make me very hesitant.
I've thought of making a new account to use with Plus, but there is also some buzz going around that makes it appear Google has coincidentally become more aggressive about pursuing and blocking "duplicate accounts". Again, anecdotes, but worrying.
1) Not just Google+ profile dependent activity, but Gmail, Calendar, Docs, etc.