I found out that about 30% of my webserver traffic are robots—programs that crawl the Internet indexing webpages. Why did I calculate that?
A question on the Robots Mailing List (dealing with programs that crawl the Internet and not mechanical devices that walk about going “R2-D2, where are you?”) asking if robots skew banner impressions and click throughs. An interesting question and while 30% might seem a bit high, that's only because my server isn't a heavily trafficked site at all, despite my good placement in the search engines.