Let me know when they start losing in the US regularly. Considering most of the successful games on the 360 are US based I don't see the big deal. They still got their deals with Square-Enix and the occasional timed exclusive JRPG, so It's not a big deal if they lose Japan. Europe they still do pretty good in even though Sony is edging them.
I think most people forget the PS3 hasn't seen such a big price cut along with a slim revision, so the pent up demand for a PS3 at a lower price was there. What if the 360 hit $100? Same thing.
By losing regularly I of course mean to the PS3 and PSP. It's obvious It's not going to catch up with the DS and Wii. Those are monsters of their own league.
I think It's already apparent what will save MS this fall: Price cut and Natal. With those two combined I see MS beating the PS3 again atleast for a few months WW.
It's just that simple.