I've always been a huge critic for bad UI designs. I always like my experience of using anything to be simple, straightforward and without any surprises. Things should work and I should find things in the easiest of ways. If I spend my time figuring out how to do things rather than doing things, I'm using the wrong UI.
That mainly is the reason for me to stick to KDE. And no matter what Microsoft says or pours into their UI designs, I just don't think they're user-friendly enough. For example, their word processing application has two options under for changing settings: there's 'Customize' and there's 'Options' under the Tools menu. Now which should I use to change my default line spacing? I always end up entering the wrong menu the first time. The woes don't end there. I have to go through each and every tab to make sure that's no the option I wanted.
Apple has always stressed a lot on their UI. I've never used one, but I've seen people use it. They still have one-button mice (atleast for the laptops). I can't imagine how just one button is sufficient for all the things I do daily. For example, in KDE, Alt + Left button and pointer movement moves windows. Alt + Right button and pointer movement resizes windows. And middle click pastes selected content. Even then, I've seen people do a lot of funky stuff with just the one button that an Apple laptop (iBook, PowerBook, etc). I'll have to actually use one to see how.
So Apple announced the iPhone. The site mentions they don't yet have FCC clearing, so it's not yet ready to be sold and to be bought. I just hope it happens very soon. That's one gadget I know I'm going to buy. I wasn't very excited with the iPod, even though it was revolutionary and all that. But this thing -- it's just too cool. In brief, the device has a phone, an iPod, a camera, ..., and an internet communicator. (For example, it's touch-screen-based and you can use two fingers to zoom into and out of a photo you're viewing.) Just go through the demos for watching videos, sending SMS, making and receiving calls, ... just about everything. It runs OS X and it's not going to cost a bomb, apparently.