Me (Squarepusher) and Themaister have been working on a Mplayer port - it already works on PS3, but the current problem is that H264 is damn slow. We're already using a shader for the YUV-to-RGB conversion, so that takes some of the load off the PPU. We don't use the SPEs due to lack of experience on that front, although to get anywhere we would obviously have to.

We will need some more experienced devs to help us out if we're going to make some progress on this.
XBMC for PS3 (PlayStation 3) port? - Page 5 - XBMC Community Forum

How come this isn't news somewhere, or front paged as a call for help to other devs