Should I use a 100mm Macro lens as a portrait lens?

Question

I am specifically considering using the Canon 100mm Macro as a portrait lens. If I want to have a macro in my bag, but not carry around a 70-200 2.8 due to weight, size, white color, or price if it is not purchased - is this a valid alternative?

Is this lens a great macro lens, but an "OK" portrait lens? Or is the performance near or on par with the typical zoom lens offerings in this range(70-200).

I understand that the 100mm Macro also has a newer more expensive L version offered. If that is much better suited to portrait work please include that in any responses.

Answer

I've used the EF 100 f/2.8 and the EF 100 f/2.8L for portraits. I find the focal length ideal for full frame and APS-H (might be a bit long for APS-C unless you're doing tight headshots). I find I need to have a macro in my arsenal and working double duty as a short tele makes either 100 particularly useful.

Stopped down in a studio setting both lenses are razor sharp and free from distortion. Here's the non L:

actual pixels, Canon EF 100mm f/2.8 Macro on 5D

On FF you get images so sharp you could cut yourself on. I bought the L version to use as a long(ish) lens for events as IS enables me to get more ambient light into the shot, but it still excels in the studio:

actual pixels, Canon 100mm f/2.8L IS Macro on 1D mkIV

Bokeh on either lens is good in my opinion (I'll dig out a sample when I get the chance), though if you want to shoot portraits with great bokeh there are better lenses (85mm f/1.2L, 135 f/2.0L).

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