I read a pretty funny post about the joys of running as root. Obviously, it’s a joke, but really it points to the joys of using an OS that does security right.
Here’s the bottom line: everything you really care about probably lives in your user space, so anything that has your privileges can stomp everything you care about. Having a privileged area off to the side that doesn’t contain stuff you care about doesn’t really get you much.
Perhaps the ideal situation is an OS that automatically backs everything up, blocks clumsy attempts to destroy the backups, and gives you pretty much free reign in user space (including the ability to easily run downloaded applications, etc.). Now, which OS does that? Hint, it’s not Vista and it’s not Linux.