One of the problems with trying to gauge the potential of ePublishing as an author is the limited amount of data out there. The big successes take up most of the spotlight, while the huge proportion of people who digitally publish slink away after a few family and friends have bought copies.
Somewhere in the middle, Tobias Buckell, whose original novels and Halo franchise books have sold well in print, has posted a careful account of how pricing and time have affected digital sales of his eBook short story collection Tides from the New Worlds. The results aren’t exactly inspiring, but they do offer some encouragement, and more importantly, some clarity. See his post here: http://www.tobiasbuckell.com/2011/04/01/a-year-of-selling-tides-from-the-new-worlds/ .