I'm starting to see more of this, and it fills up my Recent Activity list with useless comments. It would be nice if there was a way to downvote them but that is not available for comments. Would it be appropriate to flag them for moderator review?
This will create more Google fodder which will increase the traffic, which increases the chance of the proposal succeeding.
So what happens if people answer off-topic questions? No big deal - they just won't be imported when the site goes Beta.
Update: see related feature request added by me: Area51: allow answers much earlier
I don't know what proposals you're referring to, but the people putting answers on my proposals are people who should know better, like Adam Davis here (user Pollyanna on this site), so it seems like just typical meta.stackoverflow.com timewasting behaviour rather than a lack of user education.