How long has a monotonic clock been sitting in POSIX without me noticing? The lack of one has really bugged me in the past. gettimeofday is useless for many timekeeping tasks because it can jump backwards and forwards with the tides of daylight savings, NTP and switching timezones. One doesn't want every timeout to suddenly trigger because they're all `over an hour overdue`, or (possibly worse) not trigger for an hour. Usually I use settimer to increment a one second resolution counter and hope for the best.
But behold! clock_gettime (go read the manpage) can be passed a CLOCK_MONOTONIC argument and on my system at least (2.6.11, glibc CVS Jan 2005) it's a system call which returns the current uptime of the system with nanoseconds. Fantastic.
(Note: you need to link against librt.)