Just under half--48 percent--of IT decision makers in the U.S., according to a poll by IT services firm CDW.
CDW's third Windows Vista tracking poll since October 2006, this survey shows a 19 percentage-point increase in adoption since February 2007.
Vista migration is also increasing, with 35 percent of those surveyed saying they are in the process of moving to Vista. Just 12 percent said this last February. Thirteen percent of these migrations are complete and another third are due to be finished by May 2008.
CDW claimed this shows Microsoft's latest operating system isin the mainstream business market.
Of those still testing and migrating to Vista, almost half said its performance and key features are "above expectations," with the top-rated features being security, performance, productivity, search, and updates.
Mark Gambill, CDW vice president, said the past year was one of ", industry partners, and adopters alike."
Gambill added that, since people have begun to understand the benefits of the operating system, there has been a "steady move towards adoption."
The CDW survey also found an increase in Microsoft Office 2007 adoption, with 24 percent of businesses saying they'd made the move, compared to just 6 percent in the last survey.
The poll was conducted by Walker Information and covered 772 IT decision makers.
Tim Ferguson of Silicon.com reported from London.