The only really successful epublishing -- I mean, hundreds of thousands, millions of copies distributed and read -- is the bookwarez scene, where scanned-and-OCR'd books are distributed on the darknet. The only legit publishers with any success at epublishing are the ones whose books cross the Internet without technological fetter: publishers like Baen Books and my own, Tor, who are making some or all of their catalogs available in ASCII and HTML and PDF.
The hardware-dependent ebooks, the DRM use-and-copy-restricted ebooks, they're cratering. Sales measured in the tens, sometimes the hundreds. Science fiction is a niche business, but when you're selling copies by the ten, that's not even a business, it's a hobby.