Ryan Gordon posted a blurb on Icculus.org to dispel the myth that Microsoft is holding up the release of Unreal Tournament 3 Linux and Mac clients. (thanks Scibotic)
And below you can see UT3 running in both Linux and Mac
Unreal Tournament 3: Seriously, there's no conspiracy... so stop sending me email suggesting that Microsoft is paying to block this.
And below you can see UT3 running in both Linux and Mac