Macro: Canon 180mm 3.5 vs Sigma 150mm 2.8 +/- OS

I am planning to buy a tele-macro lens for my 60D, and had planned on the Canon 180mm - but now Sigma releases a slightly shorter, slightly faster aperture 1:1 macro lens with optical stabilization. I haven't seen or used either of the Sigmas (the new one was just announced and won't be out for a month or two) or the Canon. I would like to use the lens on and off tripod for macro, and off tripod as a general telephoto for non-sports applications (so I don't really need speedy AF).

Users out there - comments on these lenses?