Following a lead from Macopinion's Road Warrior, I installed a Toshiba MK4019GAX 40GB hard drive in my Pismo. I used Carbon Copy Cloner to move everything to a FireWire drive, then from the FW drive back to the 40GB drive.
Everything works just fine, except that when it awakes from sleep, it takes nearly 2 minutes for the screen to "unfreeze". With the original 20GB drive, it took only a second or two.
I've tried reinstalling the OS, zapping the PRAM, partitioning the new drive, resetting the power manager, reparing with TechTool, etc. No luck.
It behaves beautifully when booted from the FireWire drive (60GB partition).
Is there some fix I need to get things going? My old 20GB is looking better all the time.