Some PS63C7000/C8000/C77X0 owners have reported improved 50Hz black levels (and 24Hz with Cinema Smooth).
I did the firmware update just a few days ago from T-VALDEUC-2001.0 to T-VALDEUC-2004.0 (european firmwares) and there was no change in the black level.

Samsung T-VALDEUC-2004.0 vs Samsung T-VALDEUC-2001.0 firmware black level.

Although I don’t have a picture of it the black level with Cinema Smooth “on” is the same as at 50Hz.

I honestly don’t think Samsung will fix the problem (their firmware updates has only contained small and simple bug fixes and it seems to be hardware related), but I do hope I’m wrong :-)

EDIT: Just updated to the newly released 3000.6 firmware. No changes in black level on this either.