I haven't had time to do much investigation on this yet, but last night I genned FC5 from the DVD, it came up OK, then I downloaded all the latest updates which got me to 2.6.17-1.2157 and now the boot never seems to finish - it just stops printing messages really early (possibly around the time it normally switches to the graphical boot which I hadn't yet turned off). The disk doesn't seem to be running anymore and a reasonable amount of waiting didn't change anything. It isn't totally frozen - I can still hit return, and the cursor moves down one line, and Ctrl-Alt-Del reboots it.
Sound familiar to anyone?
I plan to boot in rescue mode and set the runlevel to 3 and turn off the graphical boot and see if there is anything useful laying around in dmesg or the X log. Anything else be good to poke?
This is on a asus P4C800-E with the disk on the onboard promise controller (the faster intel sata ports are already used up with another OS).