I understand that some of you are having issues with Tiger, but honestly, I have had no issues. Some wierd stuff with Safari that occasionally causes it to quit but definately not more issues than I have had with my windows XP at work. There I get frequent showstoppers that cause the entire OS to stop, like divide by zero errors and others that the OS should probably catch.
So far I know an entire mac graphic production house that has upgraded and had no trouble. I have three macs, an iMac G3 500, a G5 1.6 and a iBook G4 that I did a straight upgrade on with no issues, and I am running strange stuff like JRun, Tomcat, and JBoss on the same box, all starting at the same time with a couple of shell scripts that I tied to the login, so my setup isn't entirely standard.
All in all, it starts up faster than Panther, the finder is faster, and it has been much more reliable. Spotlight in save and open dialogs is sweet. I can network to PCs over wireless now without having the finder crap out on me. Apple has addressed all of my gripes with Panther in Tiger.
I think Apple has done a great job with this, I switched in 2001 and have no intention of going back even with the eternal lag of reasonable G5 upgrades.
If everyone here had to use a windows machine for a while, after a few complete system stop and endless reboot cycles with Service Pack 2, buggy graphics drivers, crazy network drivers, poor quality hardware from unreliable overseas vendors, you'd come home and kiss your Mac every day, minor bugs and all.