Well, this mouse lag is partly because mac os x seems to sync a lot of stuff to the update of its display which is most likely 60 Hz.
This means you get 1000/60 which is about 17ms of delay just when clicking.
There is also a prefpane app called secrets in which you can disable this 'annoying feature' called Beam Sync. (disable it and then reboot I think).
Furthermore you can set the disableosx mouse accel cvar in ioUrban terror (I looked it up in the source code and it's legit).
What I did is use USB Overdrive and disabled its acceleration option, but set the speed of the mouse cursor in the standard osx prefpane to minimum and the usb overdrive speed to max. (Using any of my mice I seriously need to loooower the sens in-game since they both top 5600 dpi). This seems to get me responses a lot closer to what I was used to back in the day using linux' low-level DGA mouse input which just mapped any pixel the mouse moved to a pixel on screen for perfect 1:1 control.
I will give this smoothmouse a try however :)
edit: looks like I'm shit out of luck since I'm still running snow leopard so it won't work
This post has been edited by l3mming: 07 January 2013 - 09:05 PM