The color rendition from this lens is just so good to look at.
How good is this lens at portraits? Moarrrr please, like angox's.
Portraits? You'll never go wrong with this lens. It's just a little bit hard in my case because it's a little bit long for an APS-C when used for portraits and the AF is slow relatively if compared to 50mm F1.8 II (for portraits).
I have been following this thread for a while, and appreciate a lot of the photos in this thread, well done to many fine photographers. I have the Canon EF 100mm macro USM (non-L).
What was written above (which I've highlighted in red font) isn't my experience. My 100mm macro's AF is definitely quicker to focus than both copies of my Canon 50mm f/1.8 II - on either of my Canon DSLR's: 7D or 350D. Not as quick as my 70-300mm L, but it's not bad... better than eg a few Sigma telephoto zooms I've used.
If I limit the AF (ie so it doesn't search through the 'macro ranges') - the 100mm AF's quite snappy, at any subject distance- particularly on my 7D, but even on my 350D. I hated the slow, grindy, inaccurate AF of the 50mm f/1.8, so I got rid of both copies.
Here are a few recent macro photos I made with my 100mm nonL lens. Note - there is also a Canon 100mm macro non-L, non-USM.... but it's quite old and not so many of those around anymore.
(PS - I have some great portraits with my 100mm macro lens too....)