I use this lens for about six months now for macro and product shooting. Working distances < 1 meter. Results are stunning and i'm more than satisfied.
On the other hand, a 100mm with a very small DOF, fixed focal length and the quality glass sould be perfect for portrait shooting as well.
However, till today i'm not able to get the sharpness i would like to see in my portraits (I always want the eyes razorsharp). Tried every setup, studio flash, hotlights, 550EX flash, daylight and almost all possible combinations on AV and TV settings. I still haven't figured it out yet, but i'll keep trying and won't give up...
Bottom line is, bought this lens for macros and this lens perfect for it.