I spent some more time using the Mac today. I customized the Terminal color scheme and behavior (the "Pro" preset was a good starting point), reduced the size of the Dock icons, and other customizations. It turns out that you really can't set a custom solid color as your background Mac OS X, and it's always been like that. A common workaround is to save a transparent PNG or TIFF image, set it to center, and then OS X will let you choose a custom desktop color.
Annoyingly, none of the visual corruption issues I had last time showed up today. It's annoying because, as a programmer, there are few things I hate worse than intermittent problems and bugs that magically fix themselves. It's a sign of a deeper issue that really needs to be fixed. The only difference between yesterday and today is I removed a USB hub from the chain connecting my mouse to the Mac, and switched to a directly-connected USB keyboard instead of sharing my model M keyboard through a PS/2-to-USB adapter.
It's too early to tell, but my first hypothesis is that the hub was drawing too much current, causing one of the 5V rails on the Mac to drop in voltage, resulting in a scrambled GPU state when switching USB devices. This hub was causing other problems, like intermittent mouse dropouts, so I won't miss it. If that's the case (and I have very little evidence either way), I have to wonder why a USB port is able to affect the GPU (the USB standard requires USB hosts to deal with power issues a bit more gracefully than that). I still have a problem with the display not coming back when the Mac goes to sleep, so I disabled sleep entirely.
I did run into some other UI issues, though. I thought I'd try typing an sftp:// URI into the Finder's "Connect to Server" dialog. sftp isn't one of the supported protocols, and a helpful error message is displayed to that effect. However, the "Connecting to Server" progress dialog never goes away. If I don't click cancel, it just sits there forever, waiting for a connection that isn't possible.
All in all today was a bit smoother, so I'll keep at it.