Among the most compelling negatives about G+ for me is that ... it's the emergent evil face of Google.
Nothing has changed my view of the company as much as it's exceptionally ham-handed dealings with real identities, real names, pseudonyms, and the like, particularly as expressed by Schmid and Gundotra (with an honorable mention to Horowitz) in the past six or eight months.
To be honest, I don't think Google even needs a social networking. They will be the kings of search, youtube, and email for the foreseeable future, and that's certainly enough to rake in billions in profit.
My own familiarity with social networks gives me a strong hope that some sort of social networking interchange protocol can be established which will enable the sort of sharing and disclosure (among friends and common interest groups) we've come to love, while limiting the exploitation by advertisers, spammers, scammers, and surveillance entities many of us have come to dislike intensely.
I see Diaspora as a very significant development to this end.