Good digital book news come in multiples of four, it seems. In 2008, one major publisher announced that e-book sales had quadrupled, while another saw a 400 percent increase in e-book sales.

As GalleyCat reported this morning, Simon & Schuster wrote a holiday memo that analyzed this tough year for publishing. That memo joined last week's Random House letter in celebrating the growth of digital books.

From the Bookseller article: "Simon & Schuster expects to have nearly quadrupled e-book sales by the end of 2008, according to its c.e.o. Carolyn Reidy. In her end-of-year letter to staff, Reidy said that in response to the growing demand the publisher was making an additional 5,000 titles available."

Digital book news from the Random House memo, via the NY Observer: "In the U.S., the biggest electronic-publishing market, our e-book sales for 2008 have grown by 400% over last year. Our e-catalog will consist of more than 15,000 Random House, Inc. titles by mid-2009, some of which are now newly available on the iPhone."