I wasn't having any issues with my Al iMac, but updated anyway. 1.2 had a weird issue with a black rectangle showing up after the first reboot, but it went away, and that was the last of it. Or so I thought. For some stupid reason I updated to 1.2.1 and now I'm having issues. Froze already, but the mouse still moved. Thought it was just a fluke. But then it did it again. It's my only machine I haven't updated to Leopard. After the rest of my apps are updated for it, or 10.5.1 rolls around (whichever is first), I think I'll go ahead and update it. Tiger was working well, except for a FireFox issue that, ironically, just got fixed right before this. Can't be hardware, because it was working fine.
Hopefully whatever new update comes out this week fixes it.