There is a little mouse sensitivity bug in 2.1.1 which causes the sensitivity not to stick. It's easy to fix.
In game Configuration under Input:
Mouse Smoothing=Off
Reduce Mouse Lag=Off
Mouse Sensitivity=2.50
MouseSmoothing=0.00
MouseAcceleration=0.00
In the RedOrchestraUser.ini file:
Home/Library/Application Support/Unreal Tournament 2004/RedOrchestra/system/RedOrchestraUser.ini
MouseSensitivity=2.50000
MouseX=Count bXAxis | Axis aMouseX Speed=0.6
MouseY=Count bYAxis | Axis aMouseY Speed=0.6
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You may fine tune these setting yourself til you find a speed that suit you.
MouseSensitivity=x.x
and
MouseX=Count bXAxis | Axis aMouseX Speed=0.x
MouseY=Count bYAxis | Axis aMouseY Speed=0.x