As lots of people have said, it all depends... Being based in the Solomons, most of our customers are Australian, and most of them seem to be pretty active divers - 100 dives/year is far from uncommon. But we may attract more committed divers in the first place, since we're in the middle of nowhere. We also get a scattering of divers who think that having between six and twelve dives makes them incredibly experienced.
I stopped logging a long time ago, but this thread did make me dig out the logbooks I filled in when I started diving again after nine months out of the water (curse you, inert gas and physics!). Between March 6 2010 and December 22 2010, I logged 246 dives. And I thought of myself as taking it easy that year...
In the years I was teaching for other shops in the Pacific, anything from 400 to 700 dives a year seemed normal and reasonable. Nowadays I tend to do fewer dives, but they're often deeper/longer decompression dives, so I probably average 300 dives a year but spend pretty near as much time underwater as I ever did - I do a lot less of the 30-40 minute OW course/guiding crazy Russians/herding 18-year-old backpacker dives than I used to.
I'd guess that for most normal, healthy, unobsessed, non-dive-shop-owning types, 100 dives/year would mean giving up a fair chunk of one day every week to diving - I'd consider that a lot. On the other hand, 12 dives a year = 'active' diver? Not too sure about that.