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I bought the Makro Planar, and I have to say that the more I stop it down, the less I like it. At f2.0 it's excellent, miles ahead of the Canon and something I'd have no reservations about shooting wide open. At f2.8 it's great, still ahead of the Canon. At 4.0, the Canon is starting to catch up, but I'm seeing more coma than I expect from the Zeiss--which is a stop slower and $1000 more expensive than the Canon. At f5.6, I don't think I can fault either the Canon or the MP in terms of sharpness or contrast, but the MP can produce some really nasty flare, whereas the Canon doesn't. The MP also produces hideous sunstars, whereas the Canon's are merely ugly.
I've made some direct comparisons between the Canon 50mm f1.4 and the Zeiss 50mm f2.0 Makro-Planar. You can download web sized layered PSDs at (warning--BIG FILES):
Coma (close focus), vignette, contrast:
http://www.dementlieu.com/users/obik/fpics/canon_50_14_zeiss_50_20_01_websize.psd (I kicked the tripod while changing lenses, so the C/Z comparison isn't perfectly centered)
Flare, contrast, medium detail:
http://www.dementlieu.com/users/obik/fpics/canon_50_14_zeiss_50_20_03_websize.psd (from f4.0--will probably reshoot)
I set the white balance in ACR (the matching it for each series), but otherwise everything is ACR default. The files were downsized with a simple bicubic reduction.
I still need to test color (first impression: "Zeiss warmth" = horrible orangeness), distortion (first impression: good), pseudo-macro capabilities (first impression: good), and skin tones (no impression yet).