It's the holy grail of macro, especially for people who are already familliar with using tubes + TC's on a regular macro lens, or use reversed lenses in front of tele lenses. A great way to get into the further magnifications is to find an old 28mm f/2.8 (or 3.5) prime and reverse-mount it on something like a 100mm macro. Assuming you have the latter, a 28mm prime + 58mm reverse ring will set you back like ~60 dollars and it's good to estimate on whether or not it's your cup of tea.