The same sales, twice as fast. Impressive, right?
Not so quick my friend. Back in 2002 PCs were shipping at the rate of 10.8m a month into a worldwide installed base of 680m. Today, in early 2007, Vista is shipping into a market where PCs are selling at 21.4m a month, and into a worldwide installed base of more than 1-billion PCs. (All figures from IDC.)
So what? So, the PC market is waaay bigger than it was in 2002 -- more or less double the size. In other words, a raw units comparison across the two products is meaningless. You need to normalize Vista numbers again market size, rather than just cheerfully reporting Vista units against XP units.
By this adjusted measure how is Microsoft doing? In the absence of better data -- like the OEM/retail/upgrade splits, which I'm betting has deteriorated -- it looks like Vista sales are tracking on par with XP, and no better than that.
MSFT 1-yr chart