Books are heavy (I've got the entire Harry Potter series in hardcover!! I could use that as ballast to keep a hot air balloon from flying away)

Book pages blow around in the wind when you're outside or if your gym has a hugemongous ceiling fan that creates a breeze in the room.

Kindles weigh something like a few to several ounces (not sure what the specs are) and the pages dont turn unless you click the Next Page button.

Kindles (the Kindle 2, which I dont have...I've got the K1 instead) can also read your book to you (in a computer voice) as long as the publisher wasnt being a jerk and had that functionality turned off for books they publish.

Plus, the Kindle is just too cool. I'm a gadget freak tho. A nerd. I love gadgety things like Kindles.