>>1
Logging in as root is like removing the doors from your car and taking a drive without seatbelts. It's fine if you don't ever make a mistake, and you can get in and out of the car much more quickly. It saves time.
However, people hose systems all the time because of silly typos, file globbing that doesn't work the way you think, spaces that don't belong, because you're in a different directory than you thought, or because some file has a weird name (like "-rf"). And if I caught an employee browsing 4chan from a root account? Bam! Fired (because of the root thing, not because of 4chan).
Besides, a bunch of GUI applications will just pop up an error if you try to run them as root. I'm not sure which distros you're talking about, maybe Linspire?
http://linuxmafia.com/faq/Security/linspire-root.html