The Pocket Site

Canonical and analyst firm RedMonk released findings of a survey sent to thousands of Ubuntu Server users. It was developed with the Ubuntu community and was completed by almost 7,000 respondents. The companies says the survey confirmed that Ubuntu was being widely used in the most common workloads (web, print, file, database and mail servers) and that it is considered mission critical by most respondents.

via Canonical and RedMonk release survey on Ubuntu Server Usage.

You can grab the review results directly from here

Update: I found an interesting comparision betweem Ubuntu and Windows performance. The author plainly states they are a Linux proponent, but tries to give a fair comparision.