I'm not sure what the relationship between valve and havoc exactly is. AFAIK valve licensed the havoc1.x engine and added new stuff and customized it for their needs.
I'm pretty sure that HL2 doesn't use havoc3 at this time. For HL3 they probably will improve the source engine including the...
Sooner or later if they wanna have success with their physX cards they need to have a open api so all physic engine can make use of hw acceleration. I think that may actually happen as soon as this year.
Having said that there is no immediate pressure to change physics engine for valve. They...
Can't tell you have to see for yourself when it's available but the lack of AA* IMHO is a major drawback and of course the performance hit will be quite noticeable too
*(no higher resolution just doesn't cut it)
It's not the same thing. No current hardware supports AA on rendering into a higher precision texture/render target. HDR does need rendering into a such higher precision texture/render target so AA is not an option. It's a hardware limitation of current graphiccards.
prt is mainly used to achieve global illumination like effects(soft-shadows,interreflection,subsurface-scattering) with dynamic lights and objects.
You will hear alot about it in the near future as many of the next gen games and engines will use this technique. It's to replace diffuse...