This lens has a terrible backfocus problems.
I tested 3 brand new lenses on 2 Canon 20D bodies.
All had exactly the same problem. Backfocus.
99 percent of the reviews here insist that this lens is soft at f/1.4. I think this "diagnosis" is wrong. It's exceptionally sharp at f1.4. The problem is that it is sharp on everything behind the focusing point.
At first I thought I had a bad one, so I exchanged it. The second one had exactly the same results, then I exchange the second one and brought another D20 camera body for the tests. All to no avail. Backfocus. Backfocus. Backfocus.
On the other hand my Canons 35mm f/2.0, 85mm f/1.8 and 70-200mm f/4.0L lenses were all perfect on my now two 20D bodies. In rare cases when I got lucky and "caught" it sharp and properly focused, then the shots looked sharp, although excessively warm.
Most of the time this lens cannot be trusted. The unnatural warmth is also annoying. I also tried 50mm f1.8 - the same results, although without the pesky warm cast. Which makes me think that 50mm lenses and 20D are simply incompatible by design.
When you step down to f/4 it gets much much much better. But we don't really buy this lens to use it at f/4. The whole idea of it is f/1.4, isn't it? That's why I am giving the lowest possible rating.
My 35mm F/2.0, however, produces excellent results, although a bit noisy and with a slower AF. In fact I did compare it with 35mm f/1.4L and I didn't see much difference, really except $900 difference in price. The same with 85mm f/1.8 USM and 85mm f/1.2L - the result are almost the same, the price $1400 less.
The 70-200 f/4L however is a completely different story. This one is just absolutely incredible. There's so much clarity and air in that glass! The color and saturation are a perfection.
Once you try it there's no way back, nothing compares to it.