I received an article from a friend few days back, which provides evidence of Microsoft platform usage in Enterprise mission critical applications.  IT provides some interesting facts. Though I can't post the full article here, gist of the same is below..

Main points

• Gartner Custom Research conducted the study, which is random sample and projectable across lorgs in US
• While this does not represent the opinion of Gartner Analysts, MS worked extensively with the analysts to create the survey and validate the methodology.
• MS have also done extensive reviews of the data with Gartner analysts, who have largely maintained J2EE + Unix dominates in the mission-critical apps space ("enterprise apps").  This data shows otherwise. 
• Since the focus of this survey is mission-critical LOB applications, this study (at request of Gartner analysts), excludes email, meaning it does not include Windows Servers running Exchange.  

The Highlights  ( all questions are for Mission Critical Apps within lorgs US Only):

• Server OS Usage (multi select) - Windows leads with 65%. Commercial Unixes combined add up to 58%
• Server OS Share (single select - primary mission critical OS) - Windows leads with 36.5%. Commercial Unixes combined add up to 35.3% .
• Application Platform Usage (multi select) - Microsoft (.net & other) leads with 41%. J2EE is right behind with 40%.
• Application Platform Share (single select - primary mission critical platform) - Microsoft leads with 25%. J2EE follows with 22%.
• Mission Critical Vendors - Microsoft leads with 25%, with IBM close behind at 24%.
• Web Services Usage & Vendor - 44% of Enterprises are doing WS, Microsoft is the clear vendor leader with 45% share, followed by IBM at 20%.
• SOA Usage & Vendor - 31% of Enterprises are doing SOA, Microsoft is the clear vendor leader with 39% share, followed by IBM at 19%.
  

       Interesting huh!!!