>Again, no other software package that I have requires the >product key code when upgrading...none.
It was required in my case for the Lightroom upgrade from 2 to 3 on four different computers. Had to enter both the new key and old key on all four. However, old key was not required on PS CS4 to CS5 upgrade. Nowadays, when purchased software is downloaded rather than distrbuted on DVD, filing copies of the purchase confirmation, invoice and license key is the only viable record of proof of purchase.