particleman - 8:09 pm on Nov 12, 2013 (gmt 0)
I ran a niche forum for a while and made few observations with Adwords. Members complained about aggressive ad placement. I setup Vbulletin to provide a pretty conservative ad placement for logged in users. Consider that logged in users probably aren't as willing to click on ads (IMO).
What I suspect for you since you are a tech forum is that a significant amount of traffic comes from searches. I had similar experience. I used much more aggressive "in post" ads for users that aren't logged in. These ads turn more of a profit since they rely on the incoming visitors from search engines looking for something in particular.
Finally, you might have to do some leg work to up your monetization. I had much more success on my forum establishing a membership system, pay to play for business forum members. Basically business members paid for a higher level membership and got the ok to talk about their services on the forum, even a vendor specific forum. Take it another step you could probably sell them advertising space directly. You likely have a lot of niche business members on your forum already, offer fair rates and you'll likely get some takers. A great way to do this is to sign up for double click for publishers and you can seamlessly run your own banners and adsense in the same ad spaces.