Maybe I'm a little late to jump on this ship but I've never had ads on any of my sites. Finally (with server expenses being what they are) I decided to try Google ads. I put them on Silverfish Longboarding, a site I created a few years back that now gets about half a million page views a month.
As much as I'd like to make a little cash off it, I'm also curious as to how people react to them and how much the bother me after they've been there for awhile. I'm also really curious to see if anyone actually clicks them. Personally in my entire Internet career I've probably clicked fewer than 20 ads. Updates to come.