As far as I know, the sponsored athletes have got them now but shops won't get them until July/August time. They were launched at London Expo and were available for purchase (£110), friend of mine bought a pair.
Got to be one of the most comfortable shoes I've ever worn and I've tried a fair few (I own a running shop!). There does seem to be quite a bit of confusion though in terms of the different models of Boost. There is the Energy Boost at £110 and the Adistar Boost at £120.
The Adistar boost has more of the Boost cushioning, Continental rubber on the outsole and a Formotion unit on the heel, so much more than £10 worth of difference in technical features. Only available in specialist running stores, whereas the Energy Boost is available in JD Sports (and other shops). Should give you an idea of the two different markets they are aiming at. Have heard that the sizing on the Energy Boost is quite far out, whereas the Adistar Boost is the normal 1/2 size compared to other brands.