I have pages on an original content site that consistently achives higher than 50% CTR. Show me ANY forum that gets that kind of CTR. The secret: non-repeat visitors who find the site by organic search -- not daily repeat visitors who get to the site from being in their "favorites" list.
To answer the original question - Adsense is not the best solution for forums, but it can work. You've got to be careful of where you place the Adsense though. The best Adsense placement for a forum is going to be either after the first post in every thread or after the last post in every thread...That's where you'll get the most clicks, because that's where people are looking. You can put Adsense in the header, footer, or sidebar of your forums, but it won't get as many clicks. Try to use CPM ads or private advertisers in those locations.
well,i have adsense on my site HERE and also have revenue share on it as well..i had 2 ppl email me and said they made a few bucks off of it..i btw dotnreally make much but was not trying to actually when i started it
i do have a forum (links on my siggy) and i don't have much problem with it since it also fits my interest, so i don't really get bored waiting clicks or so. i think forums are quite good esp if you can have members joining your forum everyday, as for my forum, i think the "newbies" usually click the ads on my forum - looking for cheap stuff for their pets.. so yeah, for me forums are okay and i believe my forum will become a success in few more months hehe and regarding the earnings, i earned between $20-$30/month for the last 2 months. Yep, my site/forum is only 2 months old so i think i should considered that earnings as "good"
I have adsense on my forum (community centre link in sig) and it does about $1 per day on average. Not a huge earner, but every little helps.