The first real review of this lens is out and it looks to be as good as advertised. I've really enjoyed my Canon 50 mm f/1.4. But I really don't use it faster than f/2, so being able to use the Sigma at f/1.4 would be a huge selling point. The size and weight are detractors, but if this lens is truly this good, the size and weight would be worth it. Plus, it takes 77 mm filters, which I already have.
If this review was for a 24 mm lens I'd pre-order in a heartbeat. Considering I just bought the 35 mm Art, I'll have to think if I really need two primes only 15 mm apart. It seems like people tend to to go with either the triumvirates of 24 mm, 50 mm and 135 mm or 35 mm, 85 mm, 135 mm and right now my primes are 14 mm, 35 mm, 50 mm, and 100 mm.
Edit. Just compared and SLRGear has the 50 f/1.4 actually sharper than the 35 f/1.4 at equivalent apertures. BTW, I will probably only keep one of the 35 mm and 50 mm primes I currently have, not both.