RedHatLinux is the biggest Linux distro out there. They're pretty popular, though lately there focus seems to have shifted to "big iron" and "enterprise"-type applications, and away from the desktop (or, more specifically, the home/small office desktop -- see the [Fedora Project]).

RedHat's a pretty decent distro. The big thing it doesn't have is automatic dependency handling, like Debian or GentooLinux. Some RPM-based distros are now doing dependency handling out of the box, using apt4rpm or urpmi (I believe Suse and Mandrake both have some form of automatic dependency handling) but RedHat still doesn't do it. You can install apt4rpm yourself, of course, but the repositories for RedHat aren't very big yet (though they do definitely have some quality stuff -- [FreshRpms] has totem RPMs, for example, and totem can be a real pain to install without apt4rpm).

Anyway, having worked as a sysadmin in a RedHat shop, I can say that RedHat is pretty good in an enterprise environment. But I'm not sure it's particularly better than most other distros would be.. the most important thing in that kind of environment is that you have a standard. The biggest benefit from using RedHat is probably that it is the biggest distro, there's lots of support available for it, both in terms of companies that will sell you "traditional" kinds of support, and in terms of a helpful userbase. (You can find pre-made RPMs for RedHat for lots of software packages, and RedHat RPMs are usually the first binary packages a software maintainer will make, for example.)