I've had no wake from sleep problems with my G4 800mhz 12 inch iBook since I returned to using the software sleep (via the Sleep command in the Apple menu) rather that the power button or closing the lid.
[robg adds: I've not experienced any of the wake from sleep issues seen in a few spots around the net, but I know it's happened to others. Here's one possible fix; feel free to share your methods and experiences in the comments.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20070313224754740