I'd say Mac OSX has shitty UI. The dock is just kludging together the taskbar concept from windows, the quicklaunch bar and the notification area into one big The problem is it doesn't do any of those very well. When I click an icon on the dock, I don't know if I'm clicking on a task or a launcher. Well I guess there's a little dot beside the icon when its a task, but that just indicates the app is loaded, not that I've had it open... many of those dots are there because MacOS decided to start that app at boot.
If you have more than one window open in a single app, There's no easy way to switch between them. I can right-click on the icon and select on, or press F9 and use expose. Expose, while it looks cool, is bad UI because it requires me to watch an animation, look at all the windows and pick out the one I want. When you use expose the windows are always in a different spot so you have to re-orient yourself everytime you use it. With a real taskbar, the button for your window is always in the same location.
If I want to open a new window for an app, I have to check for a tiny dot. If there isn't one then just click the icon on the dock. If there is a dot, then I have to right-click and select new window. If I happen to not notice the dot and just click on the icon, I get the window I had open before. FAIL.
I guess you're not supposed to have more than one window open for a single app in MacOS. except if you want to move a file to a different folder you have to have two finder windows open because MacOSX doesn't allow you to cut and paste files. Odlly copy and paste works ok, just not cut and paste. Very inconsistent.
The problem with the MacOSX UI is its constantly working against itself. You need to right-click more often in MacOSX than any other OS but apple seems to discourage right-clicking by providing single button mouses and having only one button on their laptops. Yeah you can buy another mouse or do a two-finger click but it seems like apple doesn't want you to use one button on the hardware side but makes you use two button on the software side. The dock makes it difficult to manage an application that has more than one window open, so it discourages you from having multiple windows open for a single app, but finder requires you to have two windows open to move files.
My experieince with MacOSX in general is that if you do things the way Steve Jobs thinks you should be doing things, everything works fine. But if you stray from that path, everything becomes unnecessarily difficult. The Apple slogan shouldn't be "think different" it should be "think like steve jobs".
Posting this from Ubuntu on a Macbook Pro. I tried MacOSX for three months and then had to install an OS that makes sense.