Sigma test will hopefully be wrapping up in the next week or so.
I'm still trying to get around to writing a full review but my first impression is "holy shit, this lens is one of the best lenses I've ever used!"
In fact, the IQ (IMHO) bests the Zeiss primes I've used and it's nearly as well built--it's heavy, but solid. I found autofocus to be fast on the D800E and D600 bodies I've been field testing it with.
Along with the optical engineering, I have to give a nod to the new industrial design coming from Sigma. The lens is gorgeous. It combines the purposeful look of a Zeiss or Leica with a classic modern look (I really wish Nikon would take a hint and move away from that hideous gold and crappy typeface on their lenses).
At the $900 street price, this lens is a serious bargain. It's in a small group of lenses that are almost universally renowned for their performance. As far as primes go, the Sigma 35mm f/1.4 (along with the incredible new 85mm f/1.4 and 85mm f/1.8 Nikkors) is at the top of the heap.
DxO confirms this as well.