It looks like th Unreal Tournament 3 demo might be released on FilePlanet today. Basically, it is available for pre-load to FilePlanet members, and the public can try to get into some reserve spots. I just got into a spot with no problem, but you must have FilePlanet's download manager up and running, because that application will start the download when it becomes available. You can also use Gamespy Comrade (a small application that runs on your desktop like XFire) to notify you when the download becomes available. Find all of this and other details at the Fileplanet UT3 promotional site. This game has been a long time in the making, and was supposed to be released in the spring earlier this year. I'm anxious to see where they have took Unreal Tournament 2004, which was a great multiplayer game.
UPDATE: Destructoid reports that you may be able to get this demo early using this link (click the blue box, it's a site in Norway). The queue looks long though, I'm number 791 in line.
UPDATE 2: Just got an email that Fileplanet's demo will be available at 3 PM ET.
