Although it is true that the you will give up some sound quality with wireless speakers (partially due to the frequency response of the wireless channel), they are not a bad choice for driving directly off of a lap-top, since the amplifier is basically built into each speaker.
I have a pair of Advent wireless speakers. They can either be hooked up to a headphone jack, or else to a line-level output (such as the Rec-Out jacks on a receiver, or directly to the analog outputs of a CD player). They are small 2-ways, in some fairly rugged plastic cabinets. They're not really outdoor speakers, just ones that can take a little abuse, and/or a little moisture. But they're not meant to be rained on!
The other issue, of course, is that you still have to plug these into an outlet, so whether they are better than simply running speaker wires outside is debatable.
I bring mine out to my patio for parties, so that the same music is playing both inside (from my main system) and also out on the patio from the wireless speakers. I would describe the sound as "adequate". Not much bass, due to their small size, and the highs are a tad rolled-off, but they are reasonably quiet between songs (not much hiss from the wireless link). Mine are 900 MHz. models, but I believe that there are 2.4 GHz. models that might offer a somewhat higher-bandwidth channel (for a bit broader frequency response). Since both of these frequency bands are used for cordless phone, there is the possibility of interference, but the transmitter and speakers can be tuned over a fairly broad range of carrier frequencies, to get away from any interference.
I also own a set of wireless headphones (JVC, in this case) that also operate at 900 MHz. It turns out that the either product's transmitter works with both products, so I just have the single transmitter providing the signal for both the speakers and the headphones.
