In Tiger, including latest release w/ all patches:
With Fast User Switching and Scheduled Sleep:
When the scheduled time comes up a dialog pops up to inform you and let you wait, cancel, or sleep immediately. If another user is logged in, the dialog is popped up for them (or at least it is if you switch to that user). Dismissing the scheduled sleep on your account does not dismiss it on the others, so after 10 minutes, the computer still sleeps regardless of what you are doing.
Very annoying (rdar://4225421) when I have things running and other users do too (especially the ones w/ passwords on accounts that have themselves gone to bed for the night).
What's bugging you?