It's available alright, with an excessive $40 in shipping and handling for me as a Norwegian customer. It's ridiculous that they charge almost three times as much for S&H, as for the item itself!
It will do audio if the hardware it's connected to supports audio over MiniDisplayPort. Simple as that. As I understand it, Apple's computers do currently not support audio on their MiniDisplayPort interfaces.
In case anyone is interested, the adapter from MonoPrice works. It is possible to use a new Mac with mini Display Port -> HDMI (HDCP).
I'm now going to ditch my AppleTV for a Mini. Then I can hook up my Drobo to the Mini which will be hooked up to the HDTV. But keep in mind that the mini Display Port doesn't send audio, just video.