You wouldn't expect an e-reader to be very customizable, but they've provided a rich seam of fodder for enterprising hackers.
The latest to be broken is Kobo's Glo, which has has been tweaked to run a full version of Android by a user on MobileRead's forums.
It was relatively easy, as the Glo shares a lot of DNA with the previously-cracked Tolino Shine. Naturally, the hack gives you Google Play access, so it's entirely possible to install the Kindle app on the reader.
But remember -- you'd be breaking a lot of hearts over at Kobo towers if you do.