I included the Canon 35/2.8 today when I did test pictures with the Leica 35/2 ASPH, Voigtlander 35/2.5 and Voigtlander 35/1.7.
Basically, the Canon is sharp on center and soft in the corners wide open. That improves with smaller apertures but the Voigt 35/2.5 (and the other two) are better in the corners at all apertures. Of course, the Canon has lower overall contrast and its color response is very similar to the Leica and not too similar to the Voigtlanders. Objectively, the other three are better lenses but I'm going use my Canon 35/2.8 for awhile and see how I like it for my normal projects. I haven't done the formal tests yet but it does not seem to vignette at all on the R-D1. I love the small size.
Cheers,
Sean