Epic Games has released a version 2136 patch for Unreal Tournament 2003, which will become necessary in order to play online if past precedents mean anything. Since you're no doubt eager to start the download, you can find a list of mirrors at Blue's News along with an exhaustive list of changes taken from the readme file.
Some of those changes are obvious improvements - e.g. suicides now count against the team score in team deathmatch, and the minigun spin-up time has been tweaked slightly. Other changes are less obvious but equally important - for example, in Bombing Run, if a player dies before the ball gets through the hoop, he should now be credited for the throw.
Other changes address problems in virtually every area of the game, from the requisite gameplay and AI tweaks to changes to the HUD, editor and networking. The CD check problem which had been plaguing certain gamers has also apparently been fixed, so if you were falling victim to Epic's safety measures before (and haven't returned the game in disgust) then you can look forward to actually playing it this time.