In terms of successful checkouts, what is the most important element for you to see it as a positive experience? For me it would be the integration of an online wallet, such as Paypal, or Google Checkout. This makes me feel more secure as a user, and it is ridiculously easy because I don't even have to go get my wallet and type in my information....any other ideas???

Why do you feel secure with Paypal, or Google? Is it because they haven't had a major security breach yet?