well, i calculated what i spend on shipping in a typical month at amazon, and decided that Amazon Prime, amazon's new membership that for $79.99 gets you a year of free two-day shipping, is a good deal for me.
i am forever trying to get all my purchases into bits (iTunes (music), Mobiocket Reader (pleasure reading), and Safari (work reading/reference)) - but alas there are still a bunch of things i need to buy as atoms. It's usually things like phones or game cartridges, but then also books that aren't carried by safari (which seems to be more and more these days).
they've even been really smart about it and allow you to tie in up to four household accounts into the same membership...so for instance, my wife doesn't need to use my account to enjoy the benefits.
the result is i don't really see myself driving out to the store to save on shipping anymore. a great move for amazon.