Whoa. Since upgrading to QuickTime 6.2 and iTunes 4 last night (which are totally and completely awesome), my computer has been suddenly unstable, actually even crashing every 15 minutes or so. A quick (had to be!) Google search found reports of Canon scanner drivers causing problems. There are two items placed into the Login Items that poll just for button presses on the scanner. Removing these from the Login Items will fix the polling problem and I never use the buttons anyway, just the interface in Photoshop. What is odd is that they've been in there for months with no adverse affects. Hmmm...

ok, NOT - system still unstable - crashing every 12 minutes or so...
UPDATE: methinks this is related to the known IO USB Hub bug in 10.2.5 but why it didn't appear prior to this is a mystery. I think I've got a fix for it and will try it out later tonight. Simply unplugging the hub is not a viable solution.
UPDATE 2: The USB bug was the problem. Very odd that it appeared after several weeks of running fine. You'll need to download the IOUSB kext file from 10.2.4 and install it over the 10.2.5 version and you'll be good to go until Apple releases an official update.