Its a bit hidden, and still in alpha state I think.

http://www.luxrender.net/wiki/index.php?title=Luxrender_and_OpenCL

Most of the magic is happening in the forums (including download links)

http://www.luxrender.net/forum/viewforum.php?f=34

You need to register I think.

Appearently they released v1.7beta1 just today. Yay.