mrichmon said:
But powering a MBP with a MB adapter is likely to burn out the adapter (or possibly start a fire).
Or even more likely, it will simply not charge the battery while the machine is running, and charge it very slowly when its not. This is how the old PowerBook 1400/Duo/3400c/G3/iBook adapters worked. If you connected a low power Duo power supply to an iBook or PowerBook G3, it would simply maintain the same battery level while running - no charging.
I believe this was even documented in a TIL article at Apple's web site.