I used to have reservations about buying sigma lenses...
I bought this lens as I wanted both a 1:1 macro lens and a telephoto prime lens for my canon 20D. On paper this lens appeared to fit the bill, so I took the plundge and bought one.
I was amazed by how sharp the images were stright away - even on the 20Ds small LCD screen, the difference was apparent.
Compared to my canon 17-40L and 28-105II USM, images form the 150mm Sigma require much less USM/sharpening.
Colour is neutral, and out-of-focus blur attractive. HSM is on a par with USM in terms of speed and noise (or lack of). Build quality is equal to the canon L series.
Little things like the three step focusing limiter, and including the tripod ring, lens hood and lens case make for a pleasant change.
I would highly recommend this lens both for its macro and telephoto capabilities (240mm on x1.6 CMOS)