Home Theater Magazine reviewed a wireless 5.1 system by Aperion in their last issue. It's not truly wireless, as each speaker (and sub) needs to be plugged-in to a power outlet, since they are not wired to an amp/receiver. The review was very positive, but I would very much like to see a side by side comparison of their wireless system with the traditional wired version of their Intimus system, which HTM did not do.
So, check out Aperion. You can probably read the review online.
Gear: Speakers (Paradigm Reference Studio Series): 40 v4 (front L/R), CC-690 v4 (centre), 20 v4 (surround L/R). PSA XS30 (subwoofer).
Denon AVR-X4000, Emotiva XPA-5, Samsung PN64F8500 (64" plasma), DarbeeVision Darblet DVP5000, PS3, Sony BDP-S6200, Apple TV (3rd gen.), Harmony One, Sennheiser RS180