AFAICT, that's not a real button. That's a configurable pseudo-button. In particular, there doesn't appear to be tactile feedback -- the most important part of button-pressing for those of us old-school types who like to press buttons.
Where did you get your information?
It /feels/ the same as the old trackpad thus it has tactile feedback. The entire trackpad clicks.
http://www.engadget.com/2008/10/14/apple-macbook-aluminum-an...
I asked a question in good faith. Why all the down-voting?
The copy on the apple site is ambiguous -- saying that the trackpad "is the button" could mean a lot of things, including that the trackpad acts as the button (which is how I read it). It isn't an unreasonable interpretation.
I guess they could make it more obvious that the trackpad is actually physically a button...
Followup question about sources is fair, but still seems to advance an erroneous impression based on "every source I've seen". So slight downmodding (perhaps just to zero) doesn't seem clearly abusive to me.
(I've only downmodded the original false comment, while upmodding those providing true information and details.)
Watch the video. 3/4 of the way in, they introduce the trackpad. You can clearly see that the trackpad gets recessed when you click on it.
Hell, you can probably type whole paragraphs with your eyes shut without erring. Without the feel of physical buttons, you'll inevitably drift one direction or the other. That's why BlackBerry typing is really so much better than the iPhone. When you have both in broad daylight and are staring at the buttons as you type, the difference isn't as noticeable. But on a Berry, you can text one-handed while driving (though I don't recommend it) while on an iPhone you'd slip up pretty fast. Or, more importantly, you can look at the screen exclusively as you type, as you would on a computer.
I'm not sure if this is relevant here though. Perhaps it will cause your fingers to drift upward when not looking? I really don't know.