My take on Jaguar, Mac OS X 10.2, appears in today's Seattle Times. They don't have the graphic online, which shows a few details in place. For those who want to iChat with me, I'm email@example.com, and, depending on how much time I have, I might even iChat back!
Jaguar is a huge improvement primarily in two fronts: in taking advantage of graphics processing on newer G4 machines or cards with graphics upgrades through something Apple calls Quartz Extreme; and in supporting Windows machines and virtual private networking.
Quartz Extreme fully offloads a number of calculations that formerly were split between the OS and the graphics cards. For newer graphics cards, this can result in a multi-fold improvement in rendering.
On the interconnection front, you can easily mount a Windows-style (or Unix/Linux + Samba server) volume, or share a Mac volume using SMB. Jaguar also includes a PPTP client for VPN, and the resources to build IPSec VPN clients. (Several companies I've spoken to are hard at work: by early 2003, there will be at least three packages with IPSec clients, and I'm not entirely tied into the community yet.)
Should you upgrade? If you're running 10.1, probably, sure, do it. There are a variety of speed and interface improvements that just make it worth it, and all the software out there pretty much already works under 10.2, or updates are happening. There are only a couple pieces of software that didn't put out pre-Jaguar patches, even.