the resulting images will be very soft .   It sharpens up nicely by f/4
How would you rate the sharpness of the image with the lens?
While this lens will allow you to shoot in very low light, the resulting images will be very soft.  It sharpens up nicely by f/4, but there are several zoom lenses (e.g. 24-105mm f/4L) that can match it at that aperture.  While quick, the auto focus is not very accurate.  I spent a lot of time dialing in the AF micro-adjustment on my camera (7D), and while I was able to improve the average case, the variance was just too large to yield an acceptable "keeper" rate. 