I think tomelders is talking about the legality of the plug-in, which collects personal data and provides it to another party. (Edit: Actually, on rereading, maybe he really was talking about a right of access to the Facebook data. The following stands either way.)

I'm not a lawyer, but I do spend a significant amount of time working with data protection and privacy issues in the UK. With my current understanding, I don't see how that could even possibly be permitted under the data protection and privacy laws here without the consent of those whose data you're transferring to Google+.

I suspect Google could get into trouble with the ICO (what, again?) if they are behind the plug-in, but if I were them, I'd be more worried about the European level privacy hawks. Here in the UK we're relatively forgiving, but Europe can and does slap down megacorps with significant penalties from time to time.