There's no need to pump up on opinions. There are tons of reviews on the EF 50's. Virtually everyone identifies focus shift and border softness in the 50 1.2L. Photozone is pretty reliable: http://www.photozone.de/canon_eos_ff/472-canon_50_12_5d
In fact the 50 1.2L is not as sharp as the $369 50 1.4 at any aperture, and the borders never really sharpen up at any aperture.
What you get for an extra $1130 is a slightly improved bokeh, twice the weight, a loss of resolution across the board, and a red ring. Not a very good deal.
The 50L is as sharp as the 50 1.4 most everywhere and its AF is better. The canon f/1.2 and f/1.4 have similar resolution and both do better overall (average of center and edge measurements) than the Sigma and Zeiss f/1.4 offerings. TDP also found that the f/1.2 is the best option from f/1.2 to ~f/2.8.http://www.lensrentals.com/blog/2012/01/the-great-50mm-shootoutThe nice thing I like about the lensrentals evaluation was that they used the same body.
Many reviews are done when the lenses are introduced with different bodies and comparing them can be more difficult. I'm not defending the 50L's price, but it performs as well as any Canon-mount 50mm f/1.4 lens at large apertures (f/4 and larger). I've used a canon 50 f/1.4 and the resolution was much worse from f/1.4 to f/2 (even after MFA). Maybe it was the copy I was using, but it's AF accuracy was horrible from f/1.4 to f/2. LiveView AF produced better results than phase-detect AF.
It's one thing to say that none of the fast Canon-mount 50mm primes from any manufacturer performs well outside of the center and that the canon f/1.2 and f/1.4 do well against the competition. You can then argue whether or not f/1.2, the bokeh, build quality are worth the premium price. That's fair. But I'm don't think it's fair to say that the f/1.2 loses on resolution when there really isn't a better option at large apertures for Canon shooters.