That's the question running through my mind after hearing that Amazon is . The upcoming Kindle for Android app is set to hit smartphones this summer.

Amazon's pegging the app as a "companion" to its Kindle e-reader device -- buy a Kindle, the company says, then use your phone to extend its reach -- but I'm not so sure. For most casual users, is it really worth doubling up on devices?

Now, Amazon's Kindle for Android app is far from the first e-reader-independent digital book application. There's , of course, and then a program on some quietly launched device called the iPad (I about this so-called "iPad" apparatus, but apparently it has a book-reading app of its own).

Amazon bringing its own software to , though, extends the reach of the mainstream book reading app even further. We all know about Android's on the smartphone market. With the debut of the Kindle for Android app, even users who are set on sticking with the Kindle brand can get their e-book fixes without ever putting down their phones.