Sounds easy, right? You go into Power Management and set it to sleep after 30 mins. Done deal. Well what if you've enable fast user switching? Now all-of-a-sudden your computer goes to sleep because your wife is idle on VT8 while you are active on VT7. Dammit!
Here is a work-around: don't use X to sleep the computer. Disable sleep for each profile, then:
apt-get install sleepd
mine looks like:
PARAMS="-U 1800 -u 1800 -i 22 -i 23 -s \"s2ram -f\""
The default is to hibernate which is silly for a diskless desktop, so I s2ram instead. The interrupts to watch can be discovered by:
watch -n1 cat /proc/interrupts
Now wiggle the mouse and hit keys on the keyboard to discover which interrupts increment when you do that.