Are there any public audits of the disk level encryption in Mac OS X Lion?
According to a public talk by Rich Trouton, FileVault 2 is not FIPS 140-2 validated, but "Apple's new Common Crypto implementation is just starting to undergo FIPS evaluation"

The code itself for Common Crypto is available at http://www.opensource.apple.com/ and has been all the way back to 10.4 (where I got tired of checking revisions - it probably goes back even further, but what matters is the code shipped in Lion which is available for all three lion releases 10.7, 10.7.1 and 10.7.2)