ACTUALLY once they get image ads, I don't think it will be all that intrusive on very long pages in a sidebar. I would never mix it in with content (myself) but I see that size all over the place now in sidebars on major sites. I had a Halloween (image) Amazon ad that size running for a while, and it did much better than last year.
However, the text version leaves something to be desired, definitely. I wonder if I set it to the smallest font size if it would actually serve that way. I notice Google honors my font choices only when it feels like it.