Just upgraded to Snow Leopard, it was quick and painless. I am glad they threw in a few interface changes to spice it up, it looks nicer especially being able to navigate through stacks. Even though I have an Macbook with an intergrated Intel GMA graphics that doesn't benefit from Open CL the performance overall is much snappier. At least I have a dual core processor.
While theres some immediate incompatibility with some apps, its none I use and I'm sure updates will fix them soon anyway they can't be big issues considering Snow Leopard is basically Leopard on steroids and cocaine.
Heres a link to known incompatibility issues:
http://gizmodo.com/5347769/the-mac-os-x-snow-leopard-applications-blacklistI had an aluminum iMac but gave that to my parents as a gift, their old xp sony pc was on its last legs even after I put linux on it. They love Mac now and I wanted an excuse to free myself up for an upgrade, looking forward to that fabled "Tablet" Apples been working on for years and might have out by spring. And we'll probably sell my wifes Core Duo Macbook and buy a 13" MacBook Pro for her in the spring when USB 3.0 is out.
I definitely have an issue with wanting upgrades of my products. I mean the MacBook we're using runs faster, is more reliable and has more features than the brand new laptops we use at work and its from fall 2006. But alas I want to be able to take advantage of Open CL, I find transfer rates with USB 2.0 painfully slow since I download tons of tv and movies and I'm always transferring files between my Mac and home server.