On the heels of yesterday's news about a slight dip in book sales for December, PW Daily reported on December's revenue specifically at America's bookstores, which showed a 2.7 percent gain. The Census Bureau's report also indicated that bookstore sales for all of 2007 were $16.77 billion, an uptick of 1.1 percent over the previous year.

You'll recall from yesterday's item that book sales in all markets were up 7.4 percent, and that prompted an email from an anonymous reader. "It is funny that book sales were up 7 percent, but sales at stores were up only 1 percent," this person writes. "A six percent difference is huge for a 16 billion dollar business and I can only imagine where these sales are coming from since bookstores account for the vast majority of sales. Any ideas?"

Wal-Mart certainly springs to mind; it's also never been fully clear to me whether the Census Bureau's tallying of bookstores includes Amazon.com and the Barnes & Noble website. I'm sure many of you have explanations: share them with us!