Yarb, cold pizza in the morning is manna from heaven. Microwaving cold pizza is an abomination. It gets all slimy and nasty. Leftover pizza should eaten cold (especially before noon), but if you must reheat it, use the toaster oven.
Well, I have to agree with jenn, that left-over pizza is vile. But in extreme circumstances, it CAN be eaten, re-heated in an oven, the next late-morning/early afternoon, if no other carry-out or delivery options are available and nobody in the house is capable of making bacon and eggs.