It's a nice OS, but there's still so much wrong
There are the atrocities of the Address Book and iCal whose interfaces are utterly broken by the insistence on copying real world alternatives.
Finder is still a dog. The left-hand pane listing foldings and drives is much harder to read now it has been stripped of all colour and contrast. And they still haven't fixed the basics of how data is presented in the Finder, the appearance of folder contents is still entirely random - will it be a list? a set of icons, a preview - who knows? That's the excitement / frustration of Mac OS.
And then there are the wretched animations that can't be switched off. Windows zooming out of nothing circa mid 1980s GEM and the drives me to distraction bunny-hop of a new Mail message window.
I wish Apple would get some real interface designers to work on their products rather than the kiddies who knocked up this monster.