I'd really recommend considering the TS-E 90mm f/2.8 for food/product photography - it's really the lens of choice for that application. The problem with a macro lens is DoF - it's either too thin, or you have to stop down well into apertures narrow enough to soften the image with diffraction. The tilt feature of a TS-E lens gives you control over DoF, and allows you to get a deeper DoF at wider apertures.
+1 on this.
I've been using the non-L 100 for food photography recently, and as long as it's on a tripod, it's amazingly sharp. At 1:1, it can be a little too much detail, with every piece of fuzz, every spec of dust, every pore visible. But to get more than a couple of inches of sharp DoF, I need to stop it down to F13+. I haven't really seen the image quality degrade much, but it does make the flashes work harder, or forces an ISO bump. This is why I'm seriously considering the TS-E 90 now.