On my desktop system with Ubuntu 10.04 I've been having trouble the last few months with my monitor being *very* slow to wake up after power management puts it in standby. It used to come back up right away... then it took 30 seconds... then it took a minute... now it takes nearly four minutes. I suspect the delay will only get longer over time until it just won't come back at all.
I thought first of a possible hard drive issue. Maybe the system can't read what it needs to off the drive to wake up? Once the monitor is up, however, there are no obvious issues with the drive, although it is an older one.
I don't really have any other guesses. Anybody have any ideas?