I recently decided to upgrade from Fedora Core 4 to Fedora Core 5 via yum upgrade. Everything seemed to go well, however there seemed to be a random machine lockup happening - I mean total freeze, had to power off to recover!
The machine in question is an Acer Ferrari 4005 WLMi (Acer 4000 series) laptop.
I tried several things, many hours of web searching, even looked in on #fedora on irc.freenode.net but nothing seemed to work until I re-read the the Gentoo wiki Kernel Configuration entry. Re-reading that prompted me to remove all the kernel parameters I'd used since FC4 on my machine, as the 2.6.16 kernel used in FC5 seems to have fixed all the problems that were seen on this laptop previously. It certainly cured the lock up problems!
FC4 kernel parameters that I'd used (as advised in various places on the net, including the gentoo wiki previously):
i8042.nomux noapic irqpoll acpi_irq_balance
Using those parameters on FC5 caused the machine hangs, so the gentoo forums saved the day, my machine is now stable again.
There's at least one other very nice by product of the FC5 upgrade - the new kernel allows the synaptics touch pad to operate properly. Under FC4, the touch pad missed some of the clicks from the mouse keys, this was really annoying especially when trying to drag thngs around as it would take several attempts to e.g. grab a window to move it. This seems to have been completely addressed now, no more ending up with emails in the wrong folders!