Picked up a Mighty Mouse today, out of sheer curiosity, knowing I had two weeks to return it if I was the slightest bit displeased with it. I used in with my PowerBook all afternoon at work.
The scroll ball is teeny-weeny but works just as well as any scroll wheel I have experienced. Its diagonal scrolling capabilities are fine and all for those who have a use for it. All 3 of you. But seriously, it works like a champ.
The touch sensors are not overly sensitive...99% of the time; you can rest your right finger on the mouse while left clicking and vice versa. For the four hours or so I've been using it, though, it has incorrectly registered 2 left clicks, acting as if I had right clicked. That's 2 times too many in my opinion and greatly degrades my support for Apple's use of a fancy-pants technology where the traditional, mechanical method works flawlessly. Tsk...
Speaking of clicks, I assumed prior to my purchase that the scoll ball click was independent of the left and right "touch-sensitive" clicks. I was wrong. It presses the whole mouse down as well. This explains why Apple did not add in a software action for simultaneous left and right click; the scroll ball click is both left and right click seemingly.
I was most excited about assigning the squeeze button on the sides as the Application Switcher. I did. It doesn't function as I hoped. The App Switcher pops up, but unlike command-tab, it doesn't automatically select the next application. You have to left click on the app icon you want to switch to. Additionally, what I failed to realize when daydreaming about the App Switcher assigned to a mouse button is that I use command-n frequently after switching to an app (e.g. Safari) to open a new window. Therefore, because I use a keyboard command immediately after accessing the App Switcher, I might as well stick with command-tab. That is, unless I find or make a script that automates command-n, and then assign that script to, say, the scroll ball click. I don't really want to geek out on a mouse button though.
I am happy that I can assign "Button 3" functionality to the scroll ball click, as Safari treats Button 3 as open URL in new tab. That's sped up my surfing somewhat; I no longer have to hold down command when clicking on a URL. And yes, I am aware this can be accomplished with most 3-button mice.
Message to Apple: Think different all you want. Don't do different unless practical.