According to Forrester, both XP and Vista lost enterprise share to Windows 7 in the last 12 months, but Vista was particularly hard hit, dropping from 11.3% in April 2010 to just 6.2% in March 2011. In Forrester's tracking, Vista peaked at 14% in November 2009, a month after Windows 7's debut.

"It's no surprise, but firms are abandoning Windows Vista in favor of Windows 7," said Gray.

Vista was aggressively criticized by users shortly after its January 2007 release, and panned by most reviewers and analysts.

The only bright lining in the Vista cloud, Gray added, is that because it and Windows 7 share the same code base, companies that did commit to Vista have found smooth sailing when they upgrade to Windows 7.

Microsoft retains a hegemony in the enterprise -- 87.6% of all corporate computers run one of its operating systems -- but Gray said that some companies were bending to pressure from workers who wanted to use their own machines. The trend has been dubbed by analysts as the "consumerization" of the enterprise.