I've got an innie, and my daughter has what I'd call a middie - sort of an outie that doesn't really stick out.
A recent survey of Australian belly button lint/fluff also found that 96% of respondants had innies - spookily close to the results here. It was also discovered that the most likely colour of BB lint is blue. Who would have guessed.
http://www.abc.net.au/science/k2/lint/default.htm