I just loaded one up and it played fine on my Mac. Maybe try grabbing the K-Lite Codec pack (http://www.codecguide.com/download_kl.htm) to make sure you have the right codec to view the video?
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.