The new 120-300 also looks really nice. I didn't get to hold it, but I did play with the previous version and it wasn't bad! Certainly for HALF the cost of the current Canon it should be a good deal.
I've been using the new 35 1.4 and I've got to say I'm impressed with the new sigma stuff. This is my first Sigma lens I've owned as wasn't overly convinced about the earlier stuff, but so far it's great! I'm definitely going to be considering the dock when it's released, assuming the price isn't too much, and I get more than just firmware updates and AF speed.
The 130-300 OS was a curious beast. It's big and heavy, it's AF was quite fast...but like a lot of Siggi lenses....very erratic performance. It was sharp, when it's AF performed but it's no where in the AF league of the Canon 70-200 f2.8 L IS II. But here's the kicker....it's not really a 300mm lens, at infinity it's more like a 280mm which is quite short of the claimed 300mm. But the worse news is that as the focus draws in to MFD, it's focal length drops appallingly to around 240mm....which is where I would usually want to shoot with this lens. So in my opinion, it's size bulk and cost isn't justifyable over a Canon 70-200. It's a nice lens, but very dissapointing in real world use. If you want a 300mm f2.8, look for a good used Canon copy.
The 35mm f1.4 looks like a nice lens, but I've had it with Siggi lenses. I've owned a lot of them over the years but I've come to the conclusion that one gets what one pays for.