That reminds me of what Tony once told me years ago. Something about cooking appliances taking alot of power, and the staff would somehow notice. That's why I was confused.
I was just thinking about this, at the convention, actually... I take back what I said.
I saw the hair dryer - that the hotel provided - was rated at over 1,000 W. That's enough power for a small appliance.
I noticed, too, that certain outlets were labeled with how much they could handle. (The Hilton had plugs in the lamps, for example, but they were low-power.) The outlets in the bathroom appeared to be standard 15A GFCI-type - the ones with the little "test" and "reset" buttons. It's an important difference, because these are not only safer, but may trip before the greater circuit does.
So, in theory, assuming no other restrictions, you could probably plug in a single item and use it for heating stuff up. You wouldn't want to put multiple things on there; a microwave alone will hog most of the power, so running that and just about any other heating/cooking/cooling appliance will probably blow the circuit and you'll have an unhappy hotel.
The hotels might highly discourage outside appliances anyway, because heat can lead to fire. It doesn't hurt to ask the hotel if they allow it, but personally I wouldn't do it. (I'd hate to be spending time cooking at the con, anyway!)