I've come to loathe some of the aspects of OSX as I've used it for the last few months. Reliance on the mouse (oh to be able to alt-tab through windows) and the f*ked manner in which the standard Mail package identifies attachments (ie. everything is application/octet-stream!) are at the top of the list.
On the other hand, there are some really quite brilliant applications available for OSX. OmniGraffle is the best structured graph drawing package I've ever used (and I've tried many ;). I've also just discovered Hydra, a collaborative text editing program that effortlessly shares a text editing session amongst multiple users. Sadly, it's not likely to be much real use to us until they make it usable beyond a LAN.
I've also used OmniOutliner a bit, and have written an OPML → PythonPoint XML → PDF slide presentation script. Whee! :)