Why, for me? Incentives that keep the love alive

Although I'm an avid reader, I have been reluctant to read on my iPod
touch. I have tried before, but I guess I'm a bit old fashion, loving
the smell and feel of the pages of a book.
However, I downloaded and signed up for Indigo's Kobo app for my iPod
touch a few days ago, merely to see how it worked.
Since signing up, I have received a new register discount
(immediately) as well as timely discounts like x% off books turned
movies as it is Oscar season. The incentives are pretty good. Enough
for me to not only open the email but to also highly consider
purchasing my first ebook.
So what makes an incentive good enough to keep me reading, opening and
eventually purchasing?
1. A good deal. Or at least an offer that makes me think I am getting
something great for nothing. Also, occassionally, a wonderful deal or
gift that is forward to a friend worthy. For example, khiel's will
give customers a free lipbalm once in awhile.
2. Great consistent content that makes the sight of your name in the
from field excited...or at least not sent immediately to he trash.
3. Time sensitive. The deal should only be valid for a limited time.