[g00gl3r]

To be honest I have this running on a couple of forums, but have removed it from a couple too.
It can do what it says on the tin, but you do need to have a fairly big board for it to not appear so spammy. Lot's of content pages. And make the posts per page QTY quite high, and the number of keywords it uses quite low. So I found a decent result from around 25 posts per page, and only 7 or 8 keywords in the footer. I changed the text it uses to something more suited to the forum instead of "visitors found this page by searching for".

On the forums I removed it from I did find old threads that ranked very well before had dropped off, but the new threads didn't really take a hit. I guess Google understand what's new and old, and will still rank old threads if there's not much else about the net these days. So traffic-wise not much difference.

If you have a forum that gets new threads indexed quickly anyway, it's not going to be valuable at all I'd imagine. As always, content is king eh? - So if you forum is quiet and / or new and / or is in a competitive industry, there are many better ways to increase traffic, even 'long tail' traffic.