I love all the people complaining about stealing electricity. While the idea of unsecured rigs and moving them around is the real actual issue, people seem so conditioned to just reply "stealing electricity!!!!!! you are a bad bad man" Chill out, a 6 card rig uses like $2-4/day. In hotels, you're going to stay only a few nights. Big deal....
Why don't you just call up a hotel, explain what you want to do, and ask for permission? If it violates a fair use of utilities clause, it is stealing. Theft is theft. Doesn't matter if it's a candy bar or a truck load of flat screen tv's. The dollar amount isn't what I have a problem with. The moral compass of the person who is willing to do it without permission is what I have the problem with. Slippery slope people.
Ok, so how is plugging in your laptop, phone, or toothbrush (as suggested above) not stealing? A hair dryer can use upwards of 2000w. A hotel guest could use anywhere from $0.01 to $1.00 in electricity fairly easily. Would taking 6 showers and blow drying my hair each time for 1 hour in one day be theft? No, you'd just be considered a weirdo.
Why is mining viewed differently? Where do you draw the line on energy consumption? Unless a hotel establishes a rule on maximum power consumption, what is the definition of stealing? One could make the argument that you can max out the breaker on the room for the entire time you have the room booked. As also noted above, many asian hotels only turn on the lights when you insert your room card by the door thereby establishing what acceptable energy use is: when you're in the room.
That doesn't establish what acceptable energy use is. If you want to know the answer to that question, ask the hotel chain. The entire idea is a bad idea for many other reasons that have been brought up already.