I'm posting this from my brand new sleek black MacBook.
Some initial impressions:
Some things are really zippy. Other things are pretty slow. I imagine some of the slowness is due to the Rosetta interpretation (running PowerPC code on an Intel chip), but I think some of it is also due to the number of things I'm trying to do all at once (downloading and installing new versions of various things, trying out apps to make sure they work, etc). Most things are plenty fast enough.
The keyboard isn't all I could hope for; it's a little bit rattly. But not bad, and I'm quickly getting used to it. (And it may be getting a little less rattly with use.) The key spacing is fine; I can type normally without thinking about it.
The sound volume is at least as loud as on my old computer; I can listen to iTunes without needing external speakers.
The screen is very bright and very shiny. And feels a little small. But I'm not actually using it much at the moment, because the computer's hooked up to my large external monitor. (Which led me to have a few minutes of discontent: it felt for a bit like I was still using the same computer. Which is comforting, but also disappointing when you're expecting something totally new and cool.)
Almost all my apps work fine; the only ones that don't are, of course, the Classic apps. And the only one of those that I've run in the past year or two is FrameMaker, and I already knew that would be an issue. (I haven't yet converted the FM files to more readable formats.)
Apple's system for copying stuff from an old machine to a new one works pretty well. Though I apparently lost some fonts along the way--in particular, I think New Century Schoolbook is now named Century Schoolbook, and Pages doesn't know to convert the names so it's telling me I'm missing some fonts.
The built-in iSight camera is way cool. I've used it to scan some barcodes (using Delicious Library) of books I got at WisCon, and to take a silly comic-book-style photo of myself (using Photo Booth, which has a bunch of entertaining built-in filters). The resolution, clarity of image, and frame rate seem better to me than the old external iSight, though I don't actually know the stats for either.
It's pretty quiet. Occasionally the fans start up (I guess?) and it takes me a minute or two to figure out what the odd quiet noise is. A lot quieter than my old one--though my old one's cooling system was somewhat broken, and noisier than it should've been.
Seeing the Activity Monitor application show two separate CPU-usage graphs was pretty cool, and unexpected.
Occasionally it gets into a weird state where all the windows have crufty lines around them instead of shadows. I think it happens whenever I run an OpenGL app. Unfortunate.
The two-finger trackpad-scrolling interface is nifty, as is the two-finger-tap to right-click.