As a reply to the original question:
I own the Sigma and the Canon. I bought the 85mm 1.8 based on internet reviews. "The digital picture" catched me with a remark that the best thing on the 85mm L is it's ability to remind you how good the non L already is. I droped the idea of the 100mm lens as the 1.8 sounded more important to me than the 20mm more and just for the sake of a metal ring instead a plastic ring to screw the filter in I did not want to change my mind.
I bought the Sigma 50mm instead of the Canon because I liked the Bokeh of the Sigma more and someone on E-bay sold it almost new cheaper than any used Canon.
I'm selling the 85mm canon right now while it is still one of my most loved lenses, however I never use it anymore because the Sigma 50mm and the Canon 135mm L eat up enaugh real estate in my camera bag and my idea of a need to cover the middle seemes suddenly not practical.
Really be warned, if the reach, the quality and the bokeh of the 85mm is attractive, then sooner or later the lure of the 135 will be overwhelming.
That said there is something which made the 85mm interesting: It's size and shape (without the lens hood) makes it the perfect companion when using a holster pouches for DSLR with mid sized zooms.
For example your 5DII with a 28-200 or 28-300 lens in such a holster means a lot of reach but nothing fast at hand. The 85mm fits usualy perfectly into the sidepouches of such holsters and so you have the 1.8 available when light conditions are bad.
I do not share the complaints other people have about the focus of the Sigma 50mm. I love that lens just wish it would resemble more the feeling of the Sigma 30mm 1.4 However if you should buy it, it is a heavy, huge monster in relation to just being 50mm. If I know in advance that I have the need for the 50mm I usualy keep the 5d at home and take the 60d with the Sigma 30mm 1.4 as it is a much more convinient solution. Often when carying the Sigma 50mm arround I wish to either return to my old crappy Canon 50mm 1.8 The lens hood comes with the Sigma for free and is an absolute must to control flare and IQ. As the reversed Hood covers way to much of the lens to be handeled in a convinient way you will end up carying the lens with the hood proper mounted. The result is a short prime being as bulky as the the Tamron 28-70 VC.