How does Stackoverflow serve ads? All ads have an "http://engine.adzerk.net" link followed by a list of keywords. I went to th adzerk website. There wasn't much documentation there as to how to use adzerk for your site.
I'm the founder of Adzerk - we just moved out of private beta into a public beta. If you are interested in using Adzerk on your site you can fill out the email box on the pricing page and we will be sending out more information soon.
Adzerk is an ad server built for usability, speed, and flexibility. Keep in mind that we aren't an ad network - we don't sell ads we just deliver them. (StackOverflow sells all of their own ads directly)