Yesterday, I posted about the steps you need to follow if you're going to be your own publishing company and do a paper book. One of the things I mentioned to do was secure an ISBN for your book.
Smashwords' post today Smashwords Acquires 50,000 New ISBNs explains in detail about ISBNs. Smashwords has also just purchased 50,000 ISBNs to give to the authors who use their distribution services.
Just one more reason to go the ebook route, don't you think?