Eight Differences between Parmigiano-Reggiano and Grana Padano - Saucy Dressings
Outlines the nine main differences between parmigiano reggiano v grana padano, and gives much more information on both cheeses.
triedandsupplied.com
I really enjoy both! @Marco may have some local information to pass on as to how the Italians themselves view the two cheeses.