Please note that the RHEL-6 beta released today has an older version of boost than the 1.41.0 version that will be in RHEL-6 final. (Ie, RHEL-6 will sync with F13 for libstdc++/boost.) The F13/RHEL-6 packaging has some notable improvements over RHEL-5 versions.
It would have been very nice to have GCC 4.5.0's libstdc++ in RHEL-6 (especially if we are going to have to live with it as "top of RHEL tree" for another 4 years on the server!) but the release dates didn't sync, sadly. And the backport to 4.4 based gcc's isn't feasible.
If you care about this kind of stuff please let your RH reps know.