Thanks Atropos7. Looking at 12,004 page requests so far today, 1,241 of them are Mediapartners-Google and 659 of them msnbot. That's about 10%. I dunno, that doesn't seem unreasonable.
If I look at the current monthly (183,110 pages) neither of them even show up in the top 5.
I have msnbot on a crawl-delay and have a large number of reportedly bad bots excluded in robots.txt. I suspect banning googlebot would not help my AdSense relevancy much
Thanks for the tip. Now I know where to look!