I have to laugh. Not because Apple has finally done it - they've built a two-button mouse! - but they've done it in such a way that it still can be called a one-button mouse. Best comment from Slashdot here.
I guess they didn't want to completely shut down the single-button mouse haters.
I do worry that it will be less than intuitive for those who indiscriminately click with fingers other than the index. The touch-sensitive feature is aesthetically very cool, but how the hell to explain this to the noobs who've never experienced a normal multi-button mouse? As someone who does tech support for some frighteningly ignorant users, I don't look forward to that. Touch sensitivity has proved to be a bit of a sticky wicket on the Apple flat-panel displays in the past, in that they're so sensitive they had to come up with a way to disable them. It's a bit of a non-intuitive technology, if you ask me.
Still, I expect that Apple did their homework and tested this mouse on normal users. It's such a typically cool Apple implementation of an existing technology and design. I hope it's not a flop.