Jeff has mentioned in the past that dealing directly with the advertiser is "a great model if you can get it", but I imagine getting the critical mass that will attract advertisers to a desktop application is going be difficult and some ad based funding in the interim would be great. So to my question(s):
BSA seems to provide ads for desktop apps
http://blog.buysellads.com/2010/04/using-bsa-for-selling-ads-in-a-desktop-application/