I had the 100L first, traded it cause I didn't use it much. Then bought the 100 non-L on CL. I don't see a difference in IQ, they are both great! I use it for studio product photography so the weather sealing and IS are useless.
I also like using the 100 macro as a walk-around telephoto with basically no minimum focus distance. If I'm too close, well, I just get a detail shot- as opposed to no shot.