Last year, Amazon introduced its Kindle ebook. This year, Sony introduced its ereader, which Barnes & Noble is marketing under the Nook name.
I expect consumers to support only one format, and I think Amazon's Kindle will win. I certainly hope so.
For one thing, Amazon makes it easy for authors to self-publish their books, articles, short stories, scripts, poems, whatever, on Kindle. One need only open a Kindle account. You upload your book, and set the price, and it becomes available on Amazon.com.
Amazon requires a minimum price of 99 cents. They take 35% of what you collect.
I've uploaded two of my novels onto Kindle: Vampire Nation and Manhattan Sharks.
I priced them at $1.99. I uploaded Vampire Nation in late June, and Manhattan Sharks only last week.
It's easy. Any author can do it.
Sony only recently opened itself up to self-publishers. I've yet to upload anything onto Sony, but by and by.