So my friend Lucas sent a link to what I had feared would be the case. Yes the Playstation 3 sucks as a media centre almost as bad as the Xbox 360. With only support for Mpeg2, Mpeg4 and h.264, it was always going to be pretty bad. But my plans to use Linux instead in the future when they port Xbox Media Cenre to linux.
So I get the box home, get Ubuntu 7.04 on there, open up Synaptic, and download VLC. I try some 1080i MPEG2 content from a USB external HFS+ formatted drive I have. These recordings are direct, uncompressed digital rips of DVB-C MPEG2 recorded from my Cable Box via Firewire. When the picture looks grainy and the framerate is about 10fps, I remember that the Linux kernel is running on top of a hypervisor that restricts access to certain parts of the hardware, namely the badass mother of a GPU. Without access to the graphics hardware (and without a custom kernel and apps designed for the additional six availiable SIMD cores), there is no hope of being able to decode a 1.5MB/s MPEG2 stream.
Nope the future looks to be XBMC on a slim/mini PC for me. Which reminds me, there was a good interview with some of the key developers behind XBMC project on boingboing a while ago.