Got to agree with Flybywyre - I've been using a Logitech wireless keyboard and mouse set for over three years without a hitch. Two good 'gold and black' AA batteries in each last for months (and I always keep a reasonable stock of same in the house anyway for all number of devices).
The receiver unit is plugged into a Belkin KVM switch allowing me to operate the one wireless keyboard and mouse and my 17" TFT between up to four PCs if I need to. This arrangement keeps my study neat and tidy when I'm repairing or installing new software on other PCs besides my own personal one.
I hate cables trailing unnecessarily across my work space, and would unhesitatingly recommend going wireless - provided it's with good reputable hardware, and not something cheap and nasty, which will undoubtedly give you the sort of issues mentioned in previous posts.