According to this news from Outerspace.com.br, people are reporting malfunctions of their recently bought Xbox360 units. Sometimes the console simply goes OFF after some time of use. This probably is because some kind of overheating. Other problems are that some games simply locks up and show errors screens.
That's why, even if i had the opportunity to pre-order, i would never be one of the first to "Test" the new technology in consoles, no matter what company it's from.