I've already mentioned GOTH.NET is starting to use Google's AdSense on its site.
I chose AdSense because Google caches your website, and then using the text on the page, customizes ads to that page based on the keywords it pulls out of the page (ie. whats actually being 'said' on the page).
It doesnt work as well with the forums, in fact I believe only the domain ('goth') is classifying the ads shown on the forums - though it looks like thats enough - google does not cache CGI-generated pages.
As mentioned above, yes, they were added to the forums since a lot of people bypass the main site. To give you an idea - an average day's "page impressions" before I put this on the forums was about 3500 (actually, anything from 2500 to 4250 or so). Yesterday's page impressions (being the first 'full day' it has been active on the forums) were almost 14000. Obviously the clickthrough rate (percentage of clicks to impressions) has gone down from 4-8% (averaging 5%) to something like 2%, but 2% of 14000 is still more than 5% of 3500(ish).
GOTH.NET only uses TEXT ads from google. First, they're themable, you probably noticed the ads use the same colour scheme as the rest of the GOTH.NET site - so they're not too obtrusive. Second, unlike with images, the content is always going to be reasonable - they cannot flash, use gaudy colours, crappy "art" (can we say dripping blood bars and spinning pentagrams) and all in all keep the ads 'reasonable'.
GOTH.NET does indeed get paid for clicks on the ads - and to my surprise, the ads on GOTH.NET are popular! This pays for GOTH.NET's hosting in California, the hardware upgrades I've done over time, and in future, will be used as 'seed money' to get our merchandising off the ground (yes, within a few months we will begin selling t-shirts, coffee mugs, ash trays, etc).
Personally, I'm just very glad Google has set up such a site-friendly ad system, enabling ads to be unobtrusive, and still effective!
PreZ -- Systems Administrator, GOTH.NET
I wanted to change the world, but god wouldnt give me the source code.