I bought two of these last time and I have to say I am so pleased with them. What an incredible value, I cannot imagine another speaker like this at this price that could even come close to this speakers sound quality.
Someone mentioned the range being poor, I would say that it is less than a laptop and about equal to an iPhone or iPod touch's wifi range, but it needs a steady connection, so if your iPhone's wifi sometimes cuts out in a room then the speaker won't work well.
The other thing is that I wouldn't call the sound balanced. I find them somewhat bass heavy, which some people might like, but I do kind of wish that the bass was a little less heavy. The sound quality and volume still, is pretty awesome for such a small speaker.
Lastly, Apple's iOS AirPlay implementation is pretty... slow. Streaming from iTunes works pretty well, but from iOS it takes anywhere from 3-7 seconds to start playing a song. If you don't mind sacrificing some sound quality and you already have a good speaker system, you might try a bluetooth adapter instead. Once setup it works the same way as airplay on your iPhone.
Overall it's really an incredible value at this price if you are in the market for a good speaker.