Yep, open format.
And it might become industry standard if only Amazon make it easier to open it on the Kindle. Sony have recently anounced that they'll convert their whole library to epub. Yes, sony adopting an open standard, I can barely believe it myself
Anyway most of the ebook readers, hardware and software can open it. l would keep the .pdf download for people that want to print the book, add a .epub and plain .txt formats, maybe .rtf and if you have the time convert it also to the kindle format. I like to give the customer more choices.

So you're a selfpublished sci-fi author? I want to become one myself, do you have any tips? For more than just a hobby.