I don't like it for portraits, but then again, I don't like the 70-200 either. I like to be able to shoot down towards 2.0-2.5 and I think the bokeh is pretty poor on the 100 macro as well. I used it for a wedding once, and the images were poor when I compared them with my 85mm 1.2. (To be fair, most lenses are).
If it had general portrait optics similar to the 135 2.0 or 85 1.2, it would be in everyone's kit-bag, and every canon lens would be a macro.