More on Jaguar
Jaguar is definitely faster! However, Apple's thrown a wrench in the works in terms of application switching. First, you have to turn on access for assistive devices under the Universal Access pane in the System Preferences. Apple has made it so no outside application can access Command+Tab for switching with anything other than the Dock; if you want to use 3rd party apps, you'll have to adjust your behavior to another set of keys.
LiteSwitch X doesn't seem to work correctly at all with 10.2. The switch pane flashes in and out, kind of like a strobe light, making the process painful. My personal favorite switcher, KeyboardMaestro, offers a beta version for OS X. So far, no glitches with the beta and it recognizes all my previous settings. Haven't tried LaunchBar, so I'm not sure how that functions with 10.2. I did check their site, and there's no 10.2 info, so I'm guessing the verdict is still out.
Mail is finally a real mail client. The inclusion of built in AppleScript support, along with Address Book, have me seriously considering the switch from Entourage. If I can live with a external calendar app, I may just do it.