We found out a couple weeks back that id Software is gearing up to release the Doom 3 source code. However, John Carmack's latest tweet about the subject reveals that a software patent issue has held up the release—and is forcing Carmack to re-write some of the code:
Lawyers are still skittish about the patent issue around "Carmack's reverse", so I am going to write some new code for the doom3 release.
The patent for "Carmack's reverse," a shadowing technique, happens to be owned by Creative (yes, the SoundBlaster folks). Back in 2004, id Software and Creative came to an agreement that allowed Carmack to use, uh, his technique in Doom 3 for free, so long as he implemented support for Creative's EAX audio technology in the game. At the time, Carmack stated that the alternative was to use a "two-pass algorithm that gave equivalent results at a speed hit."
Perhaps the two-pass algorithm will make a comeback in the public source code release. If that's the case, I wouldn't be too terribly worried about PC performance, considering how much powerful today's graphics processors are. Performance on mobile hardware could be another story, though.