-Not supporting smaller games. May not be a financial mistake but it hurts their image when you can only count on them for blockbusters. There is a market for games that don't go on to sell 4 million copies, you know.
-Not testing their hardware enough before launch. Had the 360 not exploding when you tried to.....use it...Sony would never have stood a chance.
-I only know about video games. I have to say that, compared to the competition, Microsoft has done a surprising amount of things right.