I've had problems with my TiBook 400 (384MB RAM) and automatic sleep ever since 10.1.1 (and maybe before that, but I just didn't notice). See this hint that I posted before for the history. After a long while, I finally figured out what was killing my timeout-to-sleep feature: burning a CD with my firewire CD-RW (Yamaha 20x10x40). Fresh off a restart, sleep would come just fine. Once I burned a CD (iTunes or Retrospect incremental backup), I'd have an insomniac TiBook. But when 10.2.4 arrived, all my problems were solved!!! Burn a CD, and it'll time out to sleep just fine. Despite some "it's about damn time" grumbling, I was very happy.
But then I discovered a new problem. If I am running a backup, and it takes long enough for the screen to dim (not go black), then the CD burner stops responding at that point! Backup progress comes to a halt, and Retrospect just keeps on waiting and waiting to hear from the burner. I tell it to stop the backup, and it waits forever for the burner to close the session. Unplug the firewire cable, and Retrospect awakens from its trance. My solution (until this bug gets fixed) is to use SleepLess to keep Energy Saver from kicking in during long backup sessions.
I've told Apple about this problem, and I have no idea if burning from some other app, or using a different FireWire device will cause the same problem. Any other app burns the CD at max speed, which doesn't give Energy Saver enough time to kick in. Retrospect seems to burn at about 10x for me.
I hope this helps someone....

