My blog post Apple Infiltrates The Enterprise: 1/5 Of Global Info Workers Use Apple Products For Work! got lots of visibility because of how hot Apple is right now, but our data is much broader than just Apple. Our Forrsights Workforce and Hardware surveys have lots more data about all types of PCs and smart devices that information workers use for work, including types of operating systems — and we even know about what personal-only devices they have.
For example, as of the fall of 2011, the top three smartphone OSes have essentially the same share of the installed base of smartphones used for work by information workers across the globe (full-time workers in companies with 20 or employees who use a PC, tablet, or smartphone for work one hour or more per day). See the chart below and the reference in the Monday, January 30, New York Times article on Blackberry in Europe.