Phoronix posted a comparison review between the performance of Mac OS X 10.8 and Ubuntu 12.04 LTS

Regardless of whether you're an Apple fan or not, by now you've likely heard the information about Mac OS X 10.8 "Mountain Lion" that began making its rounds on the Internet since last week. But how's the performance of Mac OS X 10.8 and how will it compare to the competition on the Linux side, namely Ubuntu 12.04 LTS? In this article are our first benchmarks of the developer preview release of Mac OS X 10.8 compared to Mac OS X 10.7.3 and then Ubuntu 11.10 plus the latest Ubuntu 12.04 LTS development snapshot.

  Mac OS X 10.8 vs. Ubuntu 12.04 LTS Performance