Most of those not so important.
KDE 3.4 was avaliable for FC3, and there is a lot of exitement over GNOME.
But the new thing is GCC 4.0!
I don't know why, but this latest version of GCC is causing all round problems. It has been blacklisted for miscompiling KDE applications. According to redhat, the problem has been rectified:
but it is still causing problems. Just look all over this forum.
I'd suggest waiting a while before upgrading if you have volatile data