Ryan Gordon, who
converted Unreal Tournament 2004, has written the universal update for UT 04 that you can download here (it's a 199MB bitrottent file). According to MacSoft
general manager Al Schilling, UT 04 is twice as fast on an Intel Mac that it was on its older G5 siblings.
Now go get it. w00t!
Update: Post edited for accuracy. I don't play Unreal in any of its incarnations, so forgive my ignorance.