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.
The most important tactile feedback of a button is not the spring of depression but rather the shape of the button itself. It allows you to constantly reset your bearings. When you're typing on a keypad, for example, you feel whether your finger is hitting the button square in the middle, or slightly to the left or right and adjust accordingly. You can look at the screen and type because of that.
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.
Every source I've seen -- including the linked article -- describes it as a "glass multi-touch trackpad". This does not imply that it has tactile feedback, beyond the clicky noises (which aren't tactile).
Yes, it's a glass trackpad. It's also a physical button. This was made clear in the presentation, in the description on Apple.com and in a video also on Apple.com. Here's the video, you can see the button go up and down:
"...and we actually don't hate the all-clicking trackpad much at all. (If your thumb muscle memory makes you click at the bottom where the button used to be, it works and feels pretty much the same.)"
It /feels/ the same as the old trackpad thus it has tactile feedback. The entire trackpad clicks.
IMHO, original comment (http://news.ycombinator.com/item?id=332526) should be modded to slightly negative, because it's false, even if it's an honest mistake. (I think you could stop the bleeding by acknowledging the error with an after-edit.)
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.)
I did check the apple site, but hadn't seen the video. The linked article didn't really describe it, nor did any of the half-dozen other articles I've read.
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.
