Armor downgrading in Cataclysm
You will get a stat bonus of some kind if you wear "your" armor. You can still wear cloth, mail or leather of a lower armor type if it's a big upgrade, especially if it would get sharded anyway. But the days of Holy paladins in cloth or warrior wearing leather are probably behind us.
Interesting. If this is implemented in WOTLK pre-Cataclysm patch we may be seeing changes in the best gear before Cataclysm ships. One reason to grab those plate pieces and bank them for now.