Although books are not necessarily the focus of Apple’s annual Worldwide Developers conference in San Francisco—where the new iPhone 4 was unveiled today—Apple CEO Steve Jobs announced several upgrades for the iBook e-book format and several impressive book related upgrades for the new iPhone 4.

In addition, Jobs said that more than 5 million e-books have been downloaded from the iBookstore since the iPad was launched in April. And the five major trade book houses who switched to the agency model are selling 22% of all e-books sold through the iBookstore.

The new iPhone 4 will now support Apple’s iBook format as well as the iBookstore. iPhone users can buy books through the iBookstore as well as iTunes and the App store. Apple’s iBook e-book format will be upgraded at the end of the month. The iBooks upgrade will add a native PDF reader to the format as well as a separate PDF bookshelf to organize them. The upgrade will also include bookmarks and the ability to make notes in iBook editions.

But wait, there’s more. All books purchased through the iBookstore can be downloaded wirelessly to all the user devices—Laptop, desktop, iPhone and iPad—and will synch pages read, bookmarks and notes. Apple has also unveiled a new display technology called “retina display” that ups the screen resolution of the iPhone to 326ppi (the human eye apparently can only detect 300ppi) and offers a new level of sharpness for images and text.

Jobs even compared retina display to the quality of “a fine printed book.” And all of this in addition to adding multitasking, folders and other cool stuff to the iPhone.