I noticed your nice post on defaults today. I just wanted to point
out defaults play an important role (both in software and in other
avenues, such as contracts) and have been studied by a wide range of
scholars. Here are two papers I have recently written on defaults:
(you can see the abstracts and download the papers by following the
link)

Rajiv

Kesan, J. P., & Shah, R.C. (2006). Setting Software Defaults:
Perspectives from Law, Computer Science and Behavioral Economics.
Notre Dame Law Review, 82(2), 583-634, link

Shah, R.C., & Sandvig, C. (in press). Defaults as De Facto
Regulation: The Case of Wireless Access Points. Information,
Communication and Society link

I haven’t read his papers yet, but they sound interesting and relevant to the issue of defaults.

Many fast-food joints now have customers fill their own drinks at machines that are largely unsupervised. It’s possible to refill your drink at the machine, of course, and this seems to occur fairly often and without repercussions of any sort. (It’s clearly even possible to bring your own container to fill, though they would probably object to that if they caught you doing it.)

Others still fill customer drinks for them, but offer free refills upon request.

All offer the up-front choice of small, medium, or large, or when you order a combo the option to supersize (among other things) the drink. This costs extra, and free refills obviously make it unsavvy to get any size other than either small or whatever comes in a combo without any supersizing.

A KFC near to where I live will refill a small coke TWICE without batting an eye, though push you to buy a large when you first order.

Once again, price-blind or just unsavvy consumers pay a premium, and the frugal pay a lower price for the same amount of drink…

Free refills (and free ketchup packets, or similarly) also exploit a pair of hidden social “architectures of control”.

One is that people have a limited capacity to consume such things at any given time. They get full. Condiments like ketchup are also generally undesired except in combination with a non-free food item; they taste too strong and are too minuscule to be of interest by themselves undiluted. The other is that there appears to be a social more of not taking extras to bring home. People may take ketchup packets they got from the bin but didn’t use or a half-emptied drink in a disposable cup out with them, but don’t take packets or get a free refill purely to take on the road.