I love getting book recommendations. I mean face it, I'm a book person, I love to read and I love it when someone emails me or sends me a Tweet to tell me about something new they have just discovered. That being said, there's a big difference between Tweeting about your book release and spamming your book.
If you're a Tweeter it's perfectly acceptable, and encouraged, to let all of your followers know when your book releases, when you received your new cover, or where your edits stand. Of course, it's also encouraged to let them know where you are on vacation, what you're eating for dinner, what you're reading and other more personal bits of information.
It is unacceptable to send Tweets directly to other Tweeters (starting your Tweet with an @BookEndsJessica is what does this) to tell them about a "great new read" and have it be your book. Frankly, it turns me off. If you're telling me about someone else, I'm interested and appreciate it; if you're telling me about your own book, it's spam and it's irritating, and out of irritation I will probably not read your book.