They've definately proven that they are in this "to win" and won't back down from Sony, who, let's face it - are their real competition as far as they are concerned despite what the numbers say.
When you think of all of the developers like Capcom, Konami, Square (!!!) and so forth who are developing games for the 360 it will be extremely interesting to see how it plays out.
My first inclination was to think that developers would steer clear of system exclusives this round, due to escalating production costs, but that hasn't been the case. Now we're at the point where all 3 companies have such strong exclusives that the choice for gamers is amazing - so much so that the prediction is that many homes will see 2 of the 3 competing consoles installed. That's incredible to me.
Now that Microsoft has upped the size limit for XBLA games, ultimately paving the way for a service like Sony's where we will see more Symphony Of The Night's than Geometry Wars they've sent a signal to the industry.