I've recently subscribed to Jason Calacanis' weblog and was just looking over some of his recent posts.  He mentions that the feeds on his WeblogsInc.com family of sites are now including ads.  He also mentions that Yahoo will launch Overture ads in RSS as well.  I wondered when I'd hear about this happening.  I am not against this by any stretch mind you, but I can't help but be reminded of the character in Neal Stephenson's Diamond Age who became an artifex (MS readers can substitute: "distinguished engineer" for "artifex" without any loss of information) by figuring out how to put ads on chopsticks -- the last available medium.