Twenty-one months after its initial release, what do we know about Windows Vista? That home users hate it, businesses are uninstalling it and -- according to Gartner -- it's proof that the 23-year-old Windows line is "collapsing" under its own weight.

Meanwhile, predecessor Windows XP, which Microsoft stopped shipping to retailers and the major PC makers on June 30, has belatedly become so beloved that it's garnering more calls for "unretirement" than NFL icon Brett Favre did in his wildest dreams this summer.

But all of the griping about Vista and instant nostalgia for XP covers up a dry, statistical reality: XP itself was slow to catch on with users -- maybe even slower than Vista has been thus far. For instance, in September 2003, 23 months after its release, XP was running on only 6.6 percent of corporate PCs in the US and Canada, according to data compiled by AssetMetrix, an asset-tracking vendor that was later bought by Microsoft. (That information was helpfully pointed out by a Computerworld reader.)

In comparison, Forrester Research reported that as of the end of June -- 19 months after Vista's November 2006 debut for business users -- the new operating system was running on 8.8 percent of enterprise PCs worldwide. Forrester analyst Thomas Mendel, who authored the report, wasn't impressed: He compared Vista to the ill-fated New Coke.

However, even Gartner, that prophet of Windows' doom, forecasts that Vista will be more popular at the end of this year than XP was at a similar juncture -- with 28 percent of the PC operating system installed base worldwide, vs. 22 percent for XP at the end of 2003.

"The uptake of XP was slower than people remember today," said Michael Cherry, an analyst at Directions on Microsoft. He noted that many IT managers "labeled XP a consumer-only upgrade" at first.