In case you did not follow the gossip, there is a Dx 10.1 rendering path currently in Assassins Creed PC that enables some performance gains on the few Radeon cards that support it.
Tech Report followed the controversy and they managed to get some comments out of Charles Beauchemin - lead tech guy.
TR: First, what is the nature of the "costly" "post-effect" removed in Assassin's Creed's DX10.1 implementation? Is it related to antialiasing? Tone mapping?
Beauchemin: The post-effects are used to generate a special look
to the game. This means some color correction, glow, and other visual
effects that give the unique graphical ambiance to the game. They are
also used for game play, like character selection, eagle-eye vision
TR: Does the removal of this "render pass during post-effect" in the DX10.1 have an impact on image quality in the game?
Beauchemin: With DirectX 10.1, we are able to re-use an
existing buffer to render the post-effects instead of having to render
it again with different attributes. However, with the implementation of
the retail version, we found a problem that caused the post-effects to
fail to render properly.
TR: Is this "render pass during post-effect" somehow made unnecessary by DirectX 10.1?
Beauchemin: The DirectX 10.1 API enables us to re-use one
of our depth buffers without having to render it twice, once with AA
and once without.
TR: What other image quality and/or performance enchancements does the DX10.1 code path in the game offer?
Beauchemin: There is no visual difference for the gamer. Only the performance is affected.
TR: What specific factors led to DX10.1 support's removal in patch 1?
Beauchemin: Our DX10.1 implementation was not properly
done and we didn't want the users with Vista SP1 and DX10.1-enabled
cards to have a bad gaming experience.
TR: Finally, what is the future of DX10.1 support in Assassin's Creed? Will it be restored in a future patch for the game?
Beauchemin: We are currently investigating this situation.