I use RHEL, CentOS, Scientific Linux, and Fermi Linux. The basic OS is the same code base (different logos), though Scientific and Fermi Linux have additional support for clustering, HPC applications, and better Kerberos/AFS support. For my personal workstation (8-core Intel S5000XVN mb, nVidia 8800GT video) I use CentOS. I have been running that for almost 18 months and have very few complaints about it. I support clients with RHEL, Fedora, and CentOS systems, and I do some work on the others, though my wife who works in the FermiLab computer division is much more up-to-date on the Scientific/Fermi Linux world than I am.
Anyway, I think that RHEL/CentOS should be in one forum, and Fedora in its own. As noted, the differences between RHEL and CentOS are strictly cosmetic, while Fedora really is a different beast.