yeah for HangWith. I will post a link to HangWith occasionally along with a comment when I see a post where someone is seeking someone to hangout with or 'forever alone' or something relavant to what the site does.
I don't do it very often. Only when I think the link and comment in appropriate and genuine to the thread. However, when I do and, I think, because the link it relative to the OP I always get amazing click-throughs. Again, the key is being genuine and relative to the thread. I've probably generated 20k+ site visits and well over 1k signups from reddit alone from maybe 3-4 comments posted in relavant threads.
just did the same on some forum I've been a member of for quite a while. the traffic is definitely very good - and I think in general probably a lot better than what you get from reddit.
Just as an additional comment; we just started sponsoring very small Starcraft2 tournaments and we are seeing excellent returns in clicks but also and hopefully in brand and loyalty.
There really is something to say for finding, building and participating in community.