Apple is now using Twitter to promote the United States version of their iBookstore. Apple already uses Twitter to promote content for App store apps, iTunes music, TV shows, and iTunes movies. Even though the iBookstore account was created quite some time ago, Apple appears to have just started utilizing the account.
The first tweet was actually sent out just today -
Welcome to the Apple #iBookstore on Twitter. Follow us to discover new releases, exclusive book offers, and more.