Abandoned shopping carts in the virtual world

We're deep into the middle of a new software project and Ted, my senior programmer, was looking over the O'reilly Tomcat book. (Tomcat is the JAVA web server we're using) He came across the note that "statistics place the percentage of online shopping carts that actually make it through the checkout stage at only 5-10%..." leading him to comment that "we should throw up a screen that says 'deposit a quarter' when starting a cart."

This got us going on the concept of micro-payment which lead quickly (due to the fact that we both know the state of the art is lacking) to what other ways we could disuade people from abandoning their carts and tying up the memory in our servers.

Hmmm... what if we keep track of them, and next time they come we give them one with a squeaky wheel? (audio loop with a very annoying wheel noise as the background to their shopping spree)
The problem is not just a virtual one, it really ties up RAM in the various servers if people start and then abandon a cart session. We as the architects of the system have to walk a fine line in setting the session timeout (akin to having the stock-boy come and put the cart away) between too long and having to have massive amounts of RAM in each server, and too short which might annoy customers.

In the real world, the use of some refundable deposit (the quarter or even more in some areas) is used to offset the cost of someone coming out into the parking lot to retrieve the carts left there by shoppers when they've loaded their car. It has worked to some extent as it acts both as a "tax" on those who don't return the carts and an incentive to others to grab one not properly put away and take it to use - getting the deposited quarter back when they finally finish and put it away properly themselves.

In the virtual world there are few examples of ways to get viewers/customers to "do the right thing" but with a little programming effort you never know...

At a minimum you have to have "cookies" turned on to use a cart, so we could deposit a cookie on the system that kept track of whether they had finished properly with a cart the last time, and suitably modify their next session if they didn't. The real problem is how to show them that we care about their use of our carts without actually driving them away.

The use of audio feedback is now coming of age. Most people have enough bandwidth that downloading a short piece of sound is not an issue - and many people have speakers on and the volume set at something reasonable because they listen to other things.

Scenarios:

first offence - minor squeaky wheel and an occaisional comment from "people around you" while you're shopping "hey, sounds like you got one of the bad carts - too bad people leave them lying around to get beaten up instead of putting them back when they're finished"

second offence - really wobbly wheel sound - with comments like "Oh yeah - I got that one last week but the stock-boy said it was because nobody put their carts away properly - this week I got a good one - guess he was right"

repeat offender - pop-up video of smashed cart with no wheels and slow the screen-change down to mud with agonizing noise of cart being dragged along ground each time a new product is looked at - "Gee buddy, you really should have put your cart away last time - looks like they saved that one just for you..."

Hmmm... this could get to be a new perversion for those of us stuck here programming - training the users to do the right thing - by dragging in some real-world stuff to the virtual world ;)