Everytime I read something about this lens it looks more interesting and more tempting.
I have their 50 amd 85mm f1.4's and I'm very happy with them both. I also have a Siggy 20mm f1.8 which I was very happy with on my 20D, equiv= 32mm, but it's a very different beast on my 5D so I have been toying with the idea of getting a 28 or 35mm. I doubt I'll do it though as I have sort of half convinced myself that for me the future is mirrorless.