Well .. if you want my blunt opinion: they're tacky and I kinda dislike them as the educated forum admin and webmaster I consider myself to be.
BUT ... I did have some changes of mind with a forum of mine for women. I put a link in a topsite, just because I had nothing to do that moment. Imagine I got quite a traffic from that
So ... conclusion: they might work if you have the "good" demographic. I think my webmaster members would laugh themselves sensless if seeing such a button on my forums, but the girls who are not web designers had no problem following those links.
KNOW your demographic