Seems to be a big debate over this, personally I think sales will rise. Take a look at SQRL's chart ..
http://vgchartz.com/forum/thread.php?id=48088
4 weeks after Black Friday sales are at there highest.
Christmas 2006 was on monday meaning it only had the previous day (sunday) to sell and the days after boxing day + 4 stagnent days (in comparison to the massive sales before boxing day)
Christmas 2007 was on tuesday meaning it only had 2 days to sell and boxing day + 3 stagnent days after.
Christmas 2008 is on a thursday, it has 4 days (which are the busiest of the year) to sell + friday and saturday (boxing day)
So I think christmas is positioned right this year.
We will see this time next week and I can't wait if I'm right!