I don't get it. Bryan's test at TDP is a complete blowout; not even close. The Sigma is sharper in center and much much much sharper than the 1.2L away from center and in corners, and the CA on the 50L is bad, while nearly non-existent on the Sigma.
In comparing any two other lenses, where there is no brand loyalty or investment-justification involved, that kind of test result would simply be a clear blowout, and there would be no further discussion. Not here though. Here we see the defensive comments and a retreat to the trenches of the intangibles like bokeh (which is not clearly different in any sample shot I have seen anyone point to specifically) and creaminess, and the supposed uselessness of test charts (but only for this lens).
What don't you get? I'm sure people that have the 50L love the fact that some are saying their lens sucks and that the Sigma is the bee's knees. I think it's more the attitude of some posters that are getting people to be defensive. The 50L doesn't get any worse now that the Sigma is coming out, and for many that have the 50L, the decision is not as clear cut, especially if they're waiting for the 50L II to come out before making a decision to switch the S50A.
I've tried Canon's 50 f/1.4 and have the 50L and my experience is that the 50L is better than the 50 f/1.4 wide open to about f/2.8, which is consistent with the results of LensRentals 50mm shootout while TDP shows the 50 f/1.4 to be a better performer. But the 50L AFs a lot better and can be used wide open. The 50 f/1.4's AF was not accurate from f/1.4-f/2.
With Sigma's success with the S35, I'd expect the S50 to perform well AF-wise. Over time, I'd suspect that many would trade the 50L for the S50A, but it is a bit premature when it still is not available to everyone. And if one has the 24-70 II, then the 50L would be used for portraiture/low light only, so edge/corner performance is not as important. The S50 is even better than the 24-70 II at 50mm. Is everyone now going to say that the 24-70 II sucks too for landscape and that the S50 A should be used instead?