Maybe "Googlebot" is a trademark, or maybe you are violating the usage terms the crawled sites have put in place by masquerading yourself... Could you get in to trouble? _MAYBE_? Seems like a stretch in practice though. I've come across people doing this to sites i've been an admin of relatively often, and unless you're crawling with enough intensity to cause a DoS or doing something nefarious with the content, most site owners would maybe roll their eyes and move on.