This is an important question because Federal agencies and the DoD require FIPS 140-2 certification for encryption of any sensitive or classified data (in transit and at rest). Further, "National Security Systems" (NSS - includes all classified systems) require NIAP Common Criteria (CC) evaluation at various levels... and Common Criteria (below) requires FIPS certification. CC NIST SP800-53 Rev3 (Google it) now combines Federal requirements for both NSS and non-NSS systems (CC evaluated products are still a best practice for non-NSS systems).
"Is Microsoft pursuing any security certification for BitLocker?
BitLocker Drive Encryption in Windows Vista has Federal Information Processing Standard (FIPS) 140-2 certification. BitLocker is included in the Common Criteria (EAL4+) certification process for Windows Vista, Windows Server 2008, Windows 7, and Windows Server 2008 R2."