The headline figures, that Windows 8 is the fourth most popular version of Windows sounds pretty bad for Microsoft, however Windows 8 has been on the market for just seven months and in that time it has spread to 4.27% of all desktops. That's behind Windows 7 (44.85%), Windows XP (37.74%) and Windows Vista (4.5%). But it is also means that its at 10% penetration of the Windows market.
Against the competition though, Windows 8 looks like its doing even better. Mac OS X 10.8 is on 2.97% of machines - so in seven months Windows 8 has greater penetration than Mac OS X by a factor of three to two. In fact if you add Mac OS X 10.8 and 10.7 together Windows 8 still has a greater share of the numbers. That covers all Mac OS sales and upgrades for the last two years...
Remember that NetMarketShare's numbers reflect actual usage and therefore isn't skewed by Windows 8 licences being bought and then downgraded to Windows 7.
Windows 8 may yet prove to be the giant leap forward that Microsoft promised, despite the negative publicity users apparently like it.