I occasionally do things as root, and I've tried running the Finder as root. I know it's dangerous; I think I just wanted to easily move some files, or maybe it was curiosity. In any event...
Running things as root being dangerous, so I thought it'd be good to have a visual reminder of that. I ran System preferances as root using Pseudo, and changed the appearance to grey and the highlight colour to red -- this is very different from my normal appearance. Now any application running as root is immediately obvious and I am warned.
[robg adds: Despite the visual warning, I still strongly advise not running stuff as root. It is easier, no doubt about it. It's also easy to do really stupid things that you may regret later, like deleting the wrong folder. But if you're going to use root mixed with the normal environment, you really should have some sort of visual distinction!]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050509183854288