According to: http://gs.statcounter.com/#os-ww-monthly-201101-201201 http://gs.statcounter.com/#os-ww-monthly-201101-201201 XP dropped 14% in the last year, and

According to: http://gs.statcounter.com/#os-ww-monthly-201101-201201 http://gs.statcounter.com/#os-ww-monthly-201101-201201 XP dropped 14% in the last year, and is now on 34%. So a really dumb calculation says about 2 and a half years if that keeps up, but I guess there will be a longer tail of die-hard users... hard to tell, since it's pretty unprecedented for a particular version of a major OS to be so popular for so long.