According to VG Chartz:
NPD data for the USA, covering December 2nd to January 5th 2008 has arrived. As expected, Vgchartz data was quite accurate for hardware sales for the period. Despite the historical trend of sales doubling from November to December, not all platforms followed the trend this year – and both NPD and VGC data agree on this point. The reason is in the timing – with an early Black Friday and 11 days of sales after Christmas, there was no way sales were going to double across the board from November to December. Still, PSP and PS2 did roughly double their sales from November. PS3, DS, Xbox 360 and especially the supply constrained Wii fell well short of doubling November NPD USA sales however. In fact, adjusted for the fact that Wii sold for five weeks in December vs. four weeks in November, sales were hardly up at all on an average weekly basis. NPD showed just under 250,000 Wiis sold per week in November, but for the December period, the average only bumped up to 270,000 Wiis sold per week in December. Xbox 360 jumped from under 200,000 per week in November to just over 250,000 per week in December – about a 30% increase – again no where near double. DS, despite a huge volume increase, really only increased by about 60% per week. Here are the hardware numbers as reported by NPD and VGC for December. NPD total estimates are for the USA and Canada (which hasn't been released yet) using the percentage Canadian sales made up of the portion of USA + Canada November sales.
NPD USA Est. NPD Total Vgchartz VGC/NPD Est
DS 2,470,000 2,650,310 2,876,040 1.08
Wii 1,350,000 1,453,950 1,638,849 1.13
Xbox 360 1,260,000 1,349,460 1,289,156 0.96
PS2 1,100,000 1,162,700 951,764 0.82
PSP 1,060,000 1,118,300 960,885 0.86
PS3 797,600 876,562 774,795 0.88
Well it seems VG Chartz are somehow accurate and are just off a bit in comparison with the NPD data.