Timekeeping

The timer interrupt
Generated by the hardware
1 KHz for most 2.6.12 kernels
The limit for internal timer resolution
"Jiffies" is count of timer interrupts since boot (sort of)

Arguments for a faster timer interrupt
Better timer resolution, reduced latency

Arguments for slowing it down
Reduced overhead, better battery life

HZ is configurable in 2.6.13
Current default is 250Hz

More info:
John Stultz, 1:30 Saturday, Room C