I was considering very very hard on whether to get this lens. After reading tons of reviews and carefully evaluating them, I can't find justification for the new L macro over the non-L.
Don't get me wrong, on its own, the L macro lives up to the L label. IQ is excellent and all that.
But then again, the non-L is already excellent in its IQ. Anything more, it's just viewing things in a microscopic way. In fact, if you read many (and I really mean many!!) online reviews, NO one has convincingly done a strong comparison and concluded Yes, the L macro is definitely better and worth the money. All give a very vague answer, like well, do you have $ to spend? Or they openly admit it's difficult to conclude that the L is worth the price diff.
The conclusions are that:
1. IQ wise, you'd be hard pressed to tell the diff between the L and non-L macro. If you can tell the diff very occasionally, then the L might have that slight edge, but only that VERY slight.
2. The HIS IS only works well for longer shooting distance (see point 3). So the price diff is really mainly on the extra IS feature that you get. Do you shoot in low shutter speeds or have unsteady hands? Then maybe the IS is justifiable for the many hundred $ price diff.
3. Canon claims the IS can work up to 2 stops for 1:1 magnification work. This is found to be an over-exaggeration by most users online. At best, they gain only 1 stop. Honestly, for macro work, 1 stop diff hardly helps. Even if it helps, you'd get more out of focus shots from the thin DOF than camera shake.
So for those who think you can do away with your tripod with this L macro, you'd be sorely disappointed. There's no magic here with the IS. But once you use a tripod, then this L macro is practically no different from the non-L!
I guess to conclude, this L macro will be useful if you shoot often non-macro eg portraits in low light or you shoot not-so-closeup macros (though I don't know how often you really do that given you've paid so much for a true macro lens). Then you have to decide if the few hundred $ price diff is really worth it.
Portrait wise, the L macro is still no match for the wider aperture Canon primes as far as bokeh is concerned.
But lenses being lenses, sometimes I suspect people buy the 100mm macro L cos it's simply an L (read: group pressure), instead of considering other (better?) options.
Juz my opinion... YMMV....