Just seen this on G's toolbar pages. A new button for voting on web pages via Google's toolbar version3.0. http://www.google.com/support/toolbar/bin/answer.py?answer=15626&topic=936 I personally think it's a good idea. It's only in beta and don't think it will affect serps for a long time but could help remove the black stains in search results.
Yfs1 has just pointed out to me that it's been around for a while now I just never noticed (can't find it in Firefox) but I'm gunna start using it in IE anyway...
This is perhaps as old as the google toolbar elwiki. It's also the most useless function that google has ever invented.
Google has more powerful ways to see the "retention" hence how much people like a particular site than this vote button. It definitely has no effect on the serps cuz spammers are voters too