I have 2 monitors, a keyboard, a microphone and a lot of things on my desk. Using a wired mouse is awkward, I just can't move the mouse where I would want to move it, I don't feel free. My keyboard sits there and doesn't move, so I don't care if it has a wire or not, but I admit that wireless is nicer, cleaner. My keyboard sits 2 feet away from my monitors and we can see the cable, that sucks (Das S' cable is thick too). No wire would be nice.
A good wireless keyboard should tell you you'll need to change batteries before it stops working. Keeping extra batteries is a good idea too. Keyboards don't use batteries as much as wireless mice.
I've been surprised that the receiver does most of the job, and, I think, sends the same thing that a normal wired keyboard would send. It means I can browse the BIOS' config with my wireless keyboard without any problem. Don't need the OS*to be booted, don't know about bluetooth wireless keyboards though.