I think Microsoft has an amazing line up this holiday season which other then Unreal Sony is completely lacking. Seece pointed out last year Sony's Q4 actually underperformed the rest of the year combined while Microsoft did far better. This indicates that Microsoft is way more successful and powerful at Christmas then Sony has been lately.
Another big console shipper is Kinect. Sure the device's sales have slumped since launch but if Microsoft can renew interest in the device it could shift a lot of hardware. At PAX it was apparent Microsoft is really planning to drive Kinect to the bank this holiday season and if they can succeed in reviving its performance at launch it could be an ace in their hat.
Another big factor is Black Friday and Boxing Day. In the past Wii and 360 have seen massive I mean massive hardware sales on BlackFriday, in fact the Wii flourished so well Black Friday's in the past without even being significantly on sale until last year. If Microsoft gets some retailer support and offers some unmissable deals they could be in for a lot of profits. Boxing day coming at the very end of Q4 but it has the ability to ship tons of hardware making it a very important day as well.
Lastly advertising is dismal from Sony, Microsoft has so many big strong titles this winter with a good ad campaign they could probably secure far larger sales of both hardware and software.
In the end I think it will be close considering Sony's lead. But Microsoft has a real chance of giving them a run for there money. If Kinect succeeds, the software pushes hardware, blackfriday/boxingday are smashing successes and of course Microsoft can use advertising to make the 360 appear under Christmas trees everywhere then they could very well trounce Sony!
-JC7
"In God We Trust - In Games We Play " - Joel Reimer