For eating up bandwidth.  Apparently, google represents 60% of my user visit logs.  And they crawl alllll of the time.  I wonder if sites with large files that eat up a lot of bandwidth.  It just seems like a little bit of overkill on google's part.

But then again, people can always use robots.txt

bet if they knew they were 60% of your traffic, they'd give you a lot less love. (hence: beware google analytics. i bet it's integral to PageRank 3.0)