I just bought my Canon 135mm, so unless the Sigma blows it away, I probably wouldn't immediately upgrade.
I like where Sima is going, but the limited sample size concerns me. I love my Siggy 35mm, and I really hope they can keep it up. If Sigma can deliver on another couple lenses, the could really give Canon a run or their money.
Looking forward to seeing what Sima can deliver next.