With OSX it's slightly different thinking for me personally. If there is some third party program I can't live without, and I'm not sure it will work with the new version, I'll hold off (i.e. Pro Tools). However, I have recently switched to Logic Studio, and I know that will work pretty much with any new Mac OS (it's one of Apple's Pro Apps) so my thinking changes to whether or not the new OS has improvements I'm interested in, and weigh that against potential apps not working.
In the case of 10.6, most of the programs I use were either certified to work, or were tested (or experts thought they would) work. I use mostly Apple apps (iLife, iWork, GarageBand, Logic Pro), Adobe (CS3 Premium, but even though it's not officially supported I knew it would work), and non complex third party apps which have a big chance of working with the new OS. Couple that with the improvements Apple touted and it was a no-brainer for me to upgrade. I don't regret updating on day 1.
That said, I can totally understand those who use a lot of programs that broke with Snow Leopard, and their frustration with the upgrade, or their decision to hold off. I think the decision of when to upgrade varies based on user needs for OSX, unlike Windows 98, 2000, XP and Vista where the darned thing didn't really run smooth until SP1 or later. Hopefully MS will learn with 7 (which I'm beta testing and fairly happy with).









