I've owned both versions of the 100mm macro, and kept the L version. I don't shoot weddings; my primary use for the lens is portraiture, of which I do a lot.
I moved up to the 100mm macros to replace the 85/1.8, for which the vast majority of my work was head-and-shoulders shots. While it was a great lens, I rarely used it wide open, and I was always cropping. With the 100's, I do little or no cropping, and the images look even better.
I agree with those who wrote that for macro work only, you don't really need the IS in the L version. But be aware that you may end up using whichever version you get for a lot more than just macro work. That said, most of my portrait work is in-studio with a tripod, so the IS is of no use there, either. I upgraded to the 100L for optimum image quality and the ability to use a tripod collar.
I see a lot of both versions of this lens for sale at great prices on Craigslist in my area. It seems that a lot of photogs buy one to experiment with macro, find they don't do that much of it, don't appreciate the other uses of these lenses, and sell them.