I use the Canon 60 mm macro lens a lot, and certainly it is the workhorse for macro. For super-macro, I add on the Nauticam SMC. It works fairly well, nice shots are possible. The main issue is that the working distance becomes very short, so you need a steady hand and a cooperative critter. I would love to try the 100 mm macro lens, but unfortunately this is not possible with my camera/housing combo. From what I have read, diopters work better with the 100 mm.
I may bump up my aperture from around f/16-20 to f/18-22 range when I put the diopter on, but since I am that much closer to the subject, little to no adjustment is necessary to my other settings. On ISO 200, my strobes are usually around half power. If I bump up my aperture to say 22, I may have to up strobe power to 3/4.
I would disagree with Decidedlylloyd regarding changing shutter speed. Changing shutter speed does not affect exposure in super-macro, since all your light is coming from your strobe (which fires at something faster than 1/2000 of a second, so always faster than your shutter).
To answer Capt Sinbad, regarding is 100 mm lens plus a diopter the easiest way to get into super-macro, I think the short answer is yes! ;-)