The three reasons to run RHEL (from my experience):

1.> You have third-party software that requires RHEL for support purposes.

2.> You have hardware that is exotic, and requires cooperation between RedHat and the hardware vendor to make things work, or fix problems down the road.

3.> You would rather manage machines instead of actively administrate them (for whatever reason).

I have worked for an organization that had to use RHEL for any one or combination of those three reasons. We also used CentOS on all development machines (much more Linux friendly than some of the production hardware we used), and for our own in-house servers.

KDE4 looks promising. It's been a while since I used Slackware, but I'm heading back that direction now that there's an official 64-bit version in the works.

XFCE isn't a bad choice, as it's lightweight and performs well while looking good.

http://www.userlocal.com used to be a hangout for Slackware users, but it seems they've shut down the forums and now redirect that link to http://www.linuxquestions.org.

Good stuff.