i have the logitech cordless freedom optical set. with the wireless radio-based keyboard, i have no probs at all, no lag nothing. with the cordless optical mouse, i notice some mouse lag so i when i first played UT with it, i had to tweak mouse sensitivity a little and its not as good as with corded mice, but from this i was able to get achieve the same skill i had before i went cordless.. and so now when i play on corded mice computers, im way better.
i tried having two sets of mice.. a microsoft intellimouse explorer and the logitech cordless optical mouseman and it worked until my MS mouse died. by no means will u need 2 sets of keyboards although a backup would be handy if you dont have spare batteries. but the keyboard batteries last awhile so no real worries.