does this exist for CentOS 4 ?
Yes, the EL4 repository works fine on CentOS4.
taking a wild swing, I set up /etc/yum.repos/kde-redhat.repo and for S&G's, I ran the obligatory 'yum update' to see what would happen.
It's an aggressive update to be sure.
Yes, it is.
KDE 3.5.0 (and all the dependent stuff such as qt) but also samba and openoffice.
Is anyone reporting happiness / contentment with their repo enabled and their updates installed?
I use it daily on multiple machines; I have a twin need for the stability of CentOS (update-wise) on one hand, but the features of the later Kstars (part of the 'edutainment' kdeedu package) on the other. Kstars for KDE 3.4 and above has telescope control; see my .sig for why that might be important to me.
The 3.5 update didn't really break much. However, you will have difficulty with things that use the kdesu utility, since, at least with the latest updates, su is asking a second question (about the security context) and that hangs kdesu hard (I'm sure there's a config somewhere that will eliminate the security context question, but it hasn't been important enough yet for me to look for it). Those things include the superuser mode konsole, the superuser mode konqueror, the administrator mode KDE print manager, etc. K3b, on the other hand, works perfectly.
The updates ARE quite large; a major version increase (or even a minor KDE version increase) can weigh a couple hundred meg; if it includes an update to openoffice.org (the KDE integration has to be rebuilt for each new KDE version) double the size.
It is worth it to me; I use it, and like it, on my daily use notebook, which boots into CentOS about 99% of the time. But it will triple your updates bandwidth usage, on average.
Mixing with Dag or ATrpms or Karanbir's Extras is hit and miss, though, afterwards, particularly for KDE programs, since those repos are built against the stock CentOS KDE 3.3.
KDE 3.5 is slower, unfortunately, so you don't want to do this on an old machine; the machine needs to be recent and needs to have more than 256MB RAM for sure. On one machine, going from 256MB to 512MB doubled its apparent speed; the further increase to 1GB added another 33% or so on some tasks.
YMMV.