We folks who create ebooks have been waiting for iBooks for Mac for a long time as a testing tool. Copying EPUB files from one device to another is a hassle and being able to see a book right where you've created it is frankly, this side of wonderful.
But of course, we #eprdctn people are not at all the point. Apple's release of iBooks for Mac in its new Mavericks operating system is a huge step for ebooks and EPUB because it makes EPUB available where people want to use it: on their desktops. The fact that this is the very same format—and the very same files—that works in their ereaders and tablets is icing on the cake.
Have you ever tried to send someone an ebook? It's not fun. Most normal people out in the world have never heard of EPUB and if you start explaining how to download a Firefox extension or make them buy a program to open it, they'll smile (if you're lucky) and go do something else.
Up until now, if you wanted someone to be able to open an ebook easily, you sent it in PDF format. And frankly, PDF is a dead end. It works ok on a computer, but it's miserable for reading on smaller devices. (No apologies to you PDF folks, sorry, and don't flame me in the comments. I don't care that on some Android devices, a PDF is slightly readable. I want an open, universal, flexible, standard format, and that's EPUB.)
What's PDF's great advantage? After years of downloading Adobe Acrobat Reader, most people have it on their computers, and when they double-click a PDF, something miraculous happens: it opens.
The last Pew Research Center poll about ebook reading (April 2012) says that more people read ebooks on their computers than on any other devices. In fact, 42% of the Americans who had read an ebook had read it on their computers, similar to the 41% who read on black and white ereaders, 29% on cell phones, and 23% on tablets. And that was 18 months ago, in the US.
In Spain in 2012, just to give one example in Europe, 55.8% of ebook readers use a computer to read their ebooks, compared with only 6.6% who use ereaders. According to the Spanish Publishers Guild only 9.7% even own an ereader. (I wished they gathered data about mobile phone reading, but they don't.)
At any rate, until Mavericks, if they were reading on a computer, they were reading in PDF. But Apple changes that. Not only has Apple released a fairly decent EPUB reader—that supports both EPUB2 and EPUB3, and both fixed and flowing formats—the most important thing is that iBooks for Mac is included in the Mavericks installation automatically.
That means people don't have to even know iBooks exists. You send them an EPUB file, they double-click it, and it opens.
Now, why was that so hard?