Low friction is a good idea. I've not seen a bot, but control would be the thing witrh +1's. As you are actively pissing in Googles pond. "Don't shit where you sleep" springs to mind when looking to game +1's, but with the right control a tool like this might be very useful. It would require a few accounts though.
Interested to see if anyone replies to this with a bot or service with REAL control "500 +1" type services is a dumbf^ck idea. Given that CNN, BBC, Microsoft only get a few dozen for major global news stories, the idea that some fricky little website selling Amazon crap is going to get 500 overnight ..and it's Google's own social bookmark you're doing it with.../facepalm
A really good well written bot that gives great control though. That I WOULD be interested in.