Personally I think there is no silver bullet when it comes to checkout processes. Everyone is targeting a different demographic and selling different products, knowing your customers and what they ultimately want to make their lifes as consumers of your products is the ultimate goal of any checkout procedure. I normally suggest to clients to either hire a usuability to firm to go through your checkout process and determine how long it takes to do a set list of items, and suggestions to improve. Of course you can do this with some novice computer users, as I'm sure many of has have friends with out much knowledge other than turn on the computer, browse the web and email
Watching over their shoulder and not helping in any way, taking any notes you see is another way to do this wout having to hire a usuability firm.
Basically get as much input as you can from your users and tweak, tweak, tweak!