For some good humor, check out the following posts by Jeremy Zawodny from Yahoo and Matt Cutts from Google. Jeremey points out a striking similarity between the Yahoo and Google MSIE splash pages. Google has changed the splash page to something else by now.
Matt responds in that very politically correct and polite way that Matt does and then he points out how Yahoo has been copying Google’s PPC ad layouts.
I’ve seen other examples of this sort of thing shared with me by a search engine employee and I guess it’s bound to happen. They watch each other so closely and there are so many teams involved that stuff like this can slip by. Although, the ad formats and colors are pretty hard to miss.