Brave move, I think most people expected MS to go first again.
Whilst I am interested in what the PS4 is/does, I'm still held back from a purchase by the controller (unless they do something different) and backwards compatibility. We've already seen what a hash of this Nintendo have made with regards to transferring downloads over, and whilst I expect Sony to be a little better at this with the PS4 I'll be absolutely gutted if MS don't get it bang-on. They need to be able to let you access your account, then transfer EVERYTHING straight over with no fuss. If I lose all my XBLA games and DLC for Rock Band, I'll be somewhat annoyed.
Whatever happens, I think we can expect some serious numbers here for the initial cost of these things. £350+ wouldn't surprise me, maybe more.
"Chav kids are like sand people. They're easily startled but they'll be back, and in greater numbers."