There's something to be said for familiarity. This Mac trial has taught me one valuable lesson so far and it's that a consistent UI can save users a boatload of time in relearning. It also tells me that old habits die hard. Anyway, here are a few criticisms of the Mac UI:

One mouse button is annoying annoying annoying. I should be able to do all of my mouse stuff with one hand, but now I need a second to hit the Ctrl key whenever I need a context menu (ie. right click in Windows). However, if I use my eight-million button MS Intellimouse I get the context menu on right click. But who wants to carry a mouse around with them?

Windows on a Mac are rendered semi-transparent if they are out of focus (not the window being used at the moment). While this may be a great visual cue, it reduces the visibility of onfocused windows. For example, if I am typing in an MSN Messenger message window, it is very difficult to see my user list window (nevermind the fact that the list uses bright colours and the contrast is poor - way to go MS). At the very least you should be able to disable semi-transparency. Not only for the visual reasons but also because rendering semi-transparent windows is probably graphics card intensive.

Resizing windows is a PITA. When you chose to maximize a window, it maximizes its height and not width. If you want to resize a window the only place you can do this is at the bottom right hand corner. In MS Windows you can resize a window from any edge or corner.

That's all for now, but I haven't used my Mac much yet. There are some other issues that are things I'll have to get used to, like the dock and my home directories and using Unix. More criticism, no doubt, is on the way. :)