Ads in My Feeds

I’m playing around with ads in my feeds.  I’ve enabled the Feedburner feature to insert Amazon ads in my book feeds and Overture “context based” ads in several (but not all) of my other feeds.  The ads should appear at the bottom of the feed so they should be easy to ignore if you aren’t interested in them.

I’m looking for both feedback (a) on relevance and (b) unobtrusiveness.