Fedora Core 3 is not a pretty release for Redhat. The original distribution is very buggy and if you install everything - you are looking at hundreds of megs of new downloads to fix it.
Once you get it working and download all the fixes it seems to work fine. If you are already running FC2 - I'd skip this version unless there's something in it you really want - and I can't find anything that justifies the pain.
The most painfull part of the process is the broken UDEV which is now part of the bootup process. UDEV somehow dynamically creates and deletes devices as they are hotplugged in - a good idea in theory - but only when it actually works. So your /dev directory is no longer under your control. Once they get the bugs out of UDEV I'm sure it will be nice. But FC3 is definitely out there on the bleeding edge as compared to FC2 which I considered to be a stable install.
UDEV is inserted into yor initrd by mkinitrd and if the system fails to work you end up with premission denied errors on devices like /dev/null causing services to fail to load. The UDEV shipping on the CD is a very buggy version and it needs to be upgraded immediately if not sooner.
If you install KDE without GNOME it will still set the desktop to GNOME and you end up in some bizzare default graphics shell hell. If this happens you need to edit the /etc/sysconfig/desktop file and change GNOME to KDE.
Fedora Core 3 still barely supports the reiser file system and treats it like a bastard stepchild. It also deletes my linuxconf install and changes my xinetd setting to disable it. I like linuxconf and for some reason RedHat is actively supressing it. It's almost as bad as if Microsoft upgrades were to remove Netscape.
On the up side - yum is improved - and xosview is now fixed. There's a bunch of new SELinux stuff but I'm still too chicken to even go there. Linux will probably never have the security of what Novell Netware had 15 years ago - Netware was done right. The new lean graphics shell is interesting but I have a big computer so KDE is just fine for me.
My suggestion to the Fedora Core team is to release a Fedora Core 3a version that has the fixes in it. That would save people from installing a broken version of Fedora and then having to fix it. If you want to upgrade anyway - expect some pain and suffering.