Question about wireless desktop and gaming

I am considering upgrading to either the Dell branded wireless desktop or Microsoft's new wireless desktop pro. I have heard that wireless keyboards and mice are not good for gaming because there is a lag in time between the key/mouse button click and the response. Is there any truth to this?
Do any of You wireless desktop users game and how does it perform in games like RTCW?(Return to Castle Wolfenstein)
Thanks in Advance
mapii