I upgraded to Red Hat 9 today. It was mostly painless. I had some minor configuration issues, mostly related to my known-fragile networking setup. (eth0 is a USB network adapter talking to the DSL modem, with pppoe managing the actual link.)
Right off the bat, even though I'm still using my old WindowMaker configuration, Gtk+ and Qt apps have a little more gloss. Definitely nicer fonts. Most of the previously compiled software still works, so my routine didn't have to change much. The only important thing that didn't work is ical, but I'll discuss that later.
And this is annoying:
Apr 27 21:47:59 bear kernel: application bug: spamd(6190) has SIGCHLD set to SIG_IGN but calls wait().
Apr 27 21:47:59 bear kernel: (see the NOTES section of 'man 2 wait'). Workaround activated.