Nearly 30% of logged Vista crashes were due to NVIDIA driver problems, according to a Microsoft data included in the bundle. That's some 479,326 hung systems, if you're keeping score at home, and it's in first place by a large margin -- Microsoft clocks in at number two at 17.9 percent, and ATI is fourth with 9.3 percent.
The data points in the table cover an unspecified period in 2007, and Microsoft makes no attempt to break the aggregate data down into which device drivers, specifically, returned the highest number of crashes. If the number of failures were split by month and then graphed, we'd presumably see the number of NVIDIA driver failures per month decreasing as the company slowly brought its driver issues under control.
The data clearly indicates that NVIDIA had a driver problem, but it's impossible to quantify the scope of that problem given the numbers above. NVIDIA holds a greater percentage of the market than ATI, which means that there will inevitably be a higher percentage of NVIDIA driver crashes than ATI driver crashes; however, the degree to which such market share considerations have affected the results above is hard to determine in the absence of more data. There's also the matter of data collection; Microsoft's charts do not clarify if multiple crashes from a single system each counted as separate events. In theory, NVIDIA's proportion of total driver crashes could be inflated by a relatively small handful of systems with severe driver issues.