No matter what people say here or at IGN/Gamespot/the million other video gaming sites.. the XBO will most likely be a success and Sony won't dominate the market like the did during the PS1 and PS2 days. That's over once MS established itself in the market and permanently grabbed a piece of the pie.
Well, as Sony has demonstrated in the past, even the big guys fall. It happened to Sony when they had been big the previous generation, and it can happen to MS. There's no such thing in an industry as too big to fail. It all comes down to how they market them, the PR, and word of mouth. Even Nintendo got a little too confident with their Wii U after the success of the Wii. They didn't market it properly and look at what happened. The winds can change swiftly.