I tried using it when it first came out, but found that it wasn't super-useful...I think the reason is because I try not to reply to old threads...so the favorite thing doesn't help once the thread gets old, and it's too much work, apparently, for me to keep things tidy.
I would love to be able to "like" a thread instead, and have that visible to the poster/other forum members. Sometimes I don't have time to reply, but I'd like to send a "+" to the poster letting them know I've read it and like it. Then, similar to facebook, I should be able to see the posts I've "liked".