My main motivation was speed: from the moment I think "hey, I'd like to read that book" and the moment I start the firt page of that book, it takes no more than 5 minutes and I don't have to leave my chair. Compare that to 4 weeks when I special-order books at my local specialized book store.
My second motivation was that I could finally take my personal collection of scanned books on the road with me. I've been waiting for years for a decent digital paper display, and the Pearl e-ink finally makes ebook readers worthwhile for me.
My third motivation was to carry many books with me on my bicycle when I tour, without much extra weight.
My fourth motivation was that I kind of like gadgets
