As I said in the "future" thread... I've tested with the latest build of mplayer, both standalone and with the SMplayer front end. I've tried all of the TexturedVideo, TexturedVideoSync, Textured2D, TexturedXrender, and BackingStore options in xorg.conf. No change with any of the above.
Xv is simply not running yet on the R5xx parts. Hopefully the next revision of fglrx will include support for Xv video acceleration on these cards.
Come on linzerd... don't be too harsh. They're working on full 3D acceleration, of which TexturedVideo is only a portion.
Also, I wouldn't be too quick to say that the open drivers support Xv "perfectly"... it is certainly not that yet, and the degree to which the feature implementation becomes robust and efficient remains to be seen.