We haven't added any advertising yet. As Jonathan said, it's more important to get a community going first.
However, the quick dismissal of AdSense is missing a very important point... it automatically customizes itself to every page in your site. So if you put AdSense in your banner-low AdSpot, then the ad will be more relevant to the question asked. We think this is more useful to users, especially ones coming straight in off Google with a question. They see the question, the top answer, and then a (hopefully) relevant ad for something they may want. Bounce rates for Google visitors are still in the high 90% range on our site, so it makes sense to offer them a relevant thing to click on, and it helps support the site, so everyone wins.
Additionally, banner-low spots are invisible to any user with 200 rep, so your members who are there all the time contributing anyway don't get bothered by it.
As for the sidebar ad spots, if you're planning to use those, I agree it makes more sense to run your own ads.