Many have seen
the infamous video where the video from a Vista presentation had been replaced with a screenview of the MacOS X interface but the original audio describing Vista's new features was left unaltered. Needless to say, every feature mentioned as part of the VIsta were already present in OS X, and had been there for years.
Now emails that have been submitted as evidence in a (non-Apple related) lawsuit against Microsoft show how impressed Microsoft developers were with MacOS X when it debuted. The emails focus primarily on Mac's search system 'Spotlight'.