As far as server stuff goes, I have noticed some problems with Redhat 9.0, especially with ssl. That said, I've been extremely happy with mail/web server, which runs Redhat 7.3 on my trusty pentium 133.
As a desktop user, I've found Redhat 9.0 a little easier to use than Suse. The big plus for Suse is the way they centralize configuration so much using Yast, which Redhat doesn't seem to want to do. Unfortunately, I've had too many issues with suse to use it often, these included having trouble getting ssh to forward X connections (I eventually figured out how to fix this but it was a pain in the ass), not getting sound on my dvd player, and being unable to get suse to recognize my firewire cd burner. None of these were problems with Redhat.
I've tried 3 times to install Debian with a 2.4 kernel and every time something goes wrong. I'm not sure why I seem to have so much trouble, but I eventually got sick of trying and gave up.
I've been curious to try out gentoo and slackware, but I don't think their very easy to figure out for newbies.
I haven't used Mandrake in over a year, so I don't know much about it. I hear it's pretty good though. I've been meaning to install it and try it out.
OH, and linux is linux, but there are many individual parts that make up a complete GNU/Linux server. All of these can be configured or mis-configured. The complaint people have had about Redhat is that they often brake certain parts (like with ssl). I believe someone in one of these threads mentioned before that they used a version of gcc that was not stable in one of their distributions once, a classic no-no in terms of getting other stuff to work. The flip side is that, IMHO, Redhat seems to be the only one who knows what their doing in terms of making a GUI oriented OS. The printer tool is my favorite example of what's missing from other distributions.
-Venkman