Copied below is part of a wonderful newsletter I get from John Kremer @johnkremer . He is the BEST reference for book authors – here is his contact info: 

John Kremer, editor, Book Marketing Update newsletter
author, 1001 Ways to Market Your Books, Sixth Edition
Open Horizons, P O Box 2887, Taos NM 87571
575-751-3398; Email: JohnKremer@bookmarket.com
Web: http://www.bookmarket.com

Newsletter section copied below:

Twitter matters
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BookMarket.com’s Alexa rank was 169,425 in late January. On May 3rd BookMarket.com’s Alexa rank was 89,308! That 80,000 jump was due to my Twitter activity.

As a bonus, 10% of the visitors to BookMarket.com now come directly from Twitter. That’s about 10,000 new unique visitors each month coming from Twitter. Are you on Twitter yet? Why not?

Twitter resources:

The 30-Day Twitter Challenge (how I got 9,500 followers in three months and jumped my Alexa rank 80,000 points): http://blog.book
market.com/2009/03/30-day-twitter-challenge.html

How to Get Retweeted on Twitter: http://blog.bookmarket.com/
2009/04/how-to-get-retweeted-on-twitter.html

Book Marketing Tweets: http://www.bookmarket.com/BookMarketingTweets.htm

Book Marketing Twitterview: http://www.bookmarket.com/BookMarketingTwitterview.htm

126 Ways to Tweet: http://www.bookmarket.com/50WaystoTweet.htm

reader success story: Twitter and blurbs