The PMTimer doesn't get detected in an Asus A8V Deluxe motherboard (VIA
K8T800Pro) so the system uses TSC (even when you use
the notsc kernel option). This results in problems (#174390 for example) with
dual core cpus since TSC isn't stable there.
$ dmesg
...
time.c: Using 1.193182 MHz PIT timer.
time.c: Using PIT/TSC based timekeeping.
...

Under FC5 the PMTimer is detected fine in the same motherboard (with a single
core cpu though)
$ dmesg
...
ACPI: PM-Timer IO Port: 0x808
time.c: Using 3.579545 MHz WALL PM GTOD PIT/TSC timer.
...