I've had my computer back long enough now to reliably report that it's been successfully repaired. Yes, I can conclusively say that replacing the topcase (or is it top case) and logic board has fixed all remants of narcolepsy. It hasn't fallen asleep one single time since I got it back last weekend.

For those of you that happen onto this thread (and without a doubt you've got a 1.67GHz PB -- either 15" or 17") and aren't prepared to read the 80 or 90 comments on the previous two threads, here's my recommendation to you:

• Install the little program called Temperature Monitor (it's freeware)
• Set it up to keep the trackpad sensor temperature reading in the menu bar where you can see it at a glance. Also, be sure to set the history to record.
• You can run the hardware test that came on your OSX disk, but it may or may not show anything wrong (if it does, it will likely be related to the logic board)
• You will likely notice that when the trackpad temperature starts to wildly fluctuate, and then goes up into what is equivalent to the 200-something degree farenheit range, your computer goes to black screen. (Some can get it to wake up by jiggling the space bar or the shift key. Others have had to remove the battery.)
• After you hit a phase where the computer will stay awake long enough, go to your system.log. You will see some comments like this:
  
  Jan 23 17:40:06 name-of-computer kernel[0]: Power Management received emergency overtemp signal. Going to sleep.
  
  
• Save this in a text file so that you can show the correlation between the system.log information and the temperature history (which will show a big spike in temp at the exact same time).

When you talk to Apple about it, do not let them tell you they've never heard of it (the low-level person on the phone may not have, but you can get the problem escalated to a PowerBook specialist). Feel free to send them to these threads for proof. The comments of the other two threads are filled with people having the same problem. We can actually help Apple save money by sending them to this information. It has conclusively and repeatedly been shown now that replacing the Mother Board doesn't fix the sleep problem. There's no reason to replace the keyboard, the power supply, airport, wipe the HD and/or reinstall all the software. All those things have been done and none of them help.

All that needs to be replaced is the topcase and, most likely, the logic board (though it seems some may have been fixed with topcase replacement only -- at least they haven't come back here to report problems with that repair).

I had originally thought my Powerbook was from the April batch. But when getting it repaired, I learned it was actually purchased in October, thus it was much newer than I realized. (My problems began in earnest in January when it was three months old.) This problem seems to manifest itself early in the life of these computers.

Good luck to you and happy repairing!