Yes, you can read your eBooks across a wide range of devices in addition to your nook.

From Barnes & Nobles:

All you need to do is download the free Barnes & Noble eReader app on your iPhone and iPod touch, BlackBerry® smartphone, or Windows® and Mac® laptops and desktop computers. And the eBooks purchased from BN.com will sync between your nook and other reading devices with the Barnes & Noble eReader app, so you always return to the last page you read