As much as I like to rag Sony, I expect they'll still do reasonably well. 360 isn't selling well in Japan due to lack of content.
I believe we're going to see an even split at the end of this round of the war. MS will own the US. Sony will rule Japan. Sony will possibly lead Europe, but not by much, it could go either way.
Then there's Nintendo, Who may, or may not trounce the big boys, but either way, will take bit bites out of the market.