One to skip if you don't care about Macs.
random unrelated aside: don't you love those Pale Saints songs where they do all that kooky tempo-shifting shit? Shoegazing -- a criminally underappreciated era of pop.
Since I'm about the last Mac geek in the 'hood to get around to installing Panther, I'll skip quickly over the things I've been reading everywhere else (Exposé is really cool, the Finder's still fairly ass, fast-user switching will really be useful at my house...) and touch on some other things I haven't seen mentioned as much.
I installed the Mac OS X Public Beta on this machine the day I bought it. When 10.0 shipped, I wiped the drive and reinstalled from scratch. That was the last time I did a clean install. Everything since (10.0.1-10.0.4, 10.1.0-10.1.6, 10.2.0-10.2.8) has been an upgrade install. I'm happy to say I've kept my streak alive. :) I had to tweak a few things, but I'd say that's pretty impressive. The only thing that was truly broken this time around was my Java installation, and I'll explain my fix for that in another entry (for Google's sake)
I've never really been one of those people who bitches about the metal appearance, but it's really annoying with the Finder. The combination of the iTunes-style left sidebar arrangement and the metal styling means I'm constantly confusing Finder windows with the iTunes window at first glance. Irritating, especially when I'm using the Finder to work with a directory of MP3s, in which case the confusing effect is magnified. I find it particularly goofy that, as the standard Aqua appearance continues to improve, they're de-emphasizing it. I think the current iteration of Aqua, with the (further) de-emphasized pinstripes, the return of menu separator lines, and the subtly rounded and shaded titlebars is really clean and effective. The metallic appearance just isn't as polished. The Finder's incremental file-find functionality is actually useful now, though.
Continuing on the theme of visuals, it looks like some minor tweaks were made to font rendering/hinting/metrics. Some of the default system fonts have been slightly altered -- both Lucida Grande and Cochin seem noticably narrower, for example, and slightly more readable at small sizes. Even Times New Roman seems less ugly [probably still too ugly for Sven, though ;) ] Font rendering is an area where OS X is still far beyond its competitors, IMO. (no, ClearType isn't even in the ballpark)
Under the hood, it looks like they've been playing around with the way the VM subsystem allocates new swapfiles. Previous OS X versions would create new 80 megabyte swapfiles as memory use increased. This was fine in most cases, however a machine that temporarily needed to create new swap space could create many of these files at the same time. If the machine's root drive was low on disk space, this could have catastrophic effects. (OS X has an unfortunate tendency to completely shit itself when low on disk space, and all those caches the OS uses to keep things speedy get corrupted, with nasty results.) Check man dynamic_pager for the geeky details, but the new allocation scheme is much less likely to steal the last few bytes on your hard drive than the old one, which will be a comfort for us running the OS on small drives.
I suppose the switch from Sendmail to Postfix is a good thing, though it caused me some extra work. :) MacOSX Hints set me straight, as usual. (if there were an MVP award for Mac websites, they'd get my vote.) I went ahead and set up SpamAssassin, as well, for the hell of it, to stress test the Perl 5.81 installation and to see if the Panther team had made dealing with Perl modules any better. They have.
Webkit is beginning to be deeply integrated into the OS. Both the new versions of Mail and the Help Viewer use it, for example. Webkit has improvements both major and minor. One trivial but fun example can be seen by selecting the "light" layout for this weblog (currently only in Safari 1.1 and later) -- support for soft shadows a la CSS3. Useless, but cool. Interestingly, a subset of XUL is being implemented in Webkit.
Preview knows how to deal with PostScript now (yay!) Do you know how many little old ladies we would have gladly run over back in the early 90's for transparent Postscript rendering in the old Mac OS? A whole Bill Knapp's worth. That makes cool things like the following script (jacked from macosxhints.com) possible:
Yum.#!/bin/sh man -t $1 > /tmp/$1.ps open /tmp/$1.ps
“When in doubt, print ‘em out.”
— Karl’s Programming Proverb 0x7