I bought this lens as soon as it came out. I was quite impressed that it didn't take long from product announcement, to product availability - thanks Canon. I've had it for about 2 months now.
PROS: Sharpness. Whoah is this baby sharp. For most lenses I like to stop down at least 1 stop from max aperture for added sharpness, but for me on my 5DII it is plenty sharp at f/2.8. Shooting macro, this is far too shallow a DoF, so tend to shoot around f/9 - f/11, and even use a stacker to increase the DoF.
For portrait I thought maybe I might need a larger aperture (say f/2) but when I saw the shallow DoF for 100mm f/2.8, I was very happy. This brings me to my next high praise point:
Bokeh. With 9 blade circular aperture (9 blades!), this lens is second to none in the bokeh dept. Background blur is super creamy. I have a distinct disliking for pentagon/hexagon bokeh and 'unwrapped condom' circular bokeh. This lens has none of those failings - truly a great portrait lens - but better suited to full frame portraits being 100mm.
Hybrid IS. Doesn't mean anything much for extreme macro because it can't stop that in-out shallow DoF focussing issue, so close macro work really needs a tripod, but still a benefit for not-too-extreme handheld macro. For handheld portraits though it is really great.
Colour/contrast is superb. It's weather sealed with a filter in place.
Nit-picking. The plastic beyond the focus ring does seem a bit 'plasticy' but I am sure they put light plastic there so as not to unbalance the lens and make it too front-heavy, since hybrid IS probably adds to the front-end weight. I think this is the right choice, and don't think that a tripod collar is necessary. The lens does have a quality feel about it, and I'm not just talking about the red ring.
I haven't noticed any CA or distortion. I micro-adjusted the lens but found it was spot on.
A 77mm filter thread would be nice so I could use my current CP filter, but that's a minor gripe. The hybrid IS makes a bit of a squeal noise at times, but this is nothing to worry about. Sometimes I forget to change the focus range when going from portrait to macro and vice versa, but that's a 'dumb operator' issue! As for price - I think it's totally worth the money (and I don't say that about all Canon lenses). I couldn't care less if Canon discontinue the non-L 100mm macro. This is worth the added money for sure.
This lens works wonderfully with the extension tubes (I have the 25mm). If you are serious about macro - I feel you really need to get an extension tube as well to boost the magnification.
All in all a great lens, and I'd probably now rate it as my favorite. For full frame - go out and get one now!