Amazon today started offering its Kindle MatchBook service to customers in the United States, allowing them to inexpensively upgrade from some paper-based books they purchased in the past to Kindle e-book versions. This bridging of physical and virtual products is a unique strength of Amazon, and Kindle MatchBook is the firm's second major initiative of this type.

As you might imagine, Kindle MatchBook requires publisher participation, so the number of books you see from your own account will vary wildly. (And international users will need to wait longer because of the differences in book licensing from country to country.) But the idea is solid: Some of the books you purchased over the years from Amazon in traditional paper-based form can now be repurchased in Kindle format, and very cheaply: The prices range from free (allegedly) to $2.99.

In my own Kindle MatchBook list, I see 13 titles. 11 of them are priced at $2.99 and two are priced at $1.99. It's easy to see how old the purchases over—Amazon says they can be p to 18 years old—and my oldest on the list is from September 2000: In the Beginning ... was the Command Line by Neal Stephenson.  (Humorously, one of them is one of my own books, Windows XP Home Networking. It's not clear why I purchased it, but I did, on November 29, 2004.)

Of the books I see in my own list, I'll probably snag all five Neal Stephenson books I see on there at a total cost of about $17. But I'm curious to see what's added in the future too. According to Amazon, HarperCollins, Macmillan, Houghton Mifflin Harcourt, Amazon Publishing, Wiley, Chronicle Books, and Marvel are all on board currently.

Kindle MatchBook follows in the footsteps of AutoRip, which provides free MP3 versions of music you purchase (new or in the past) in CD form from Amazon. When that service went live, the selection I saw there was a little more personally embarrassing, but I recently used this service for a new purchase recently, unexpectedly, because a favorite band released a new CD/DVD combo and I wanted both the music and the concert video.

As noted, this is a unique Amazon strength: Apple, Google, and Microsoft also offer digital music (and in the case of Apple and Google, e-books) but neither has the years-long physical goods/customer relationship that Amazon does. Amazon also offers other hybrid physical/virtual services, like Amazon Prime, a yearly subscription which offers two-day shipping on virtually everything Amazon sells; subscribers also get free access to Amazon's Netflix-like Prime Instant Video service.