Trolley Spotting.co.uk is a fantastic little website (found via Linkbunnies.org so thanks Bunnies), which aims to document abandonded shopping trolleys in three cities: Nottingham, Portsmouth and, of course, London.
The site's creator explains:
Trolley Spotting started when I lived in Islington, north London and became aware of the many supermarket trolleys that were abandoned on the street...I was fascinated by the way people would park them, carefully placing them against a wall or wheeling them between cars.
In order to satisfy this trolley obsession the site acts as a 'day-to-day data exhibition' whereby the 'migration' of the trolleys is captured on film while virtual maps plot their course.
It doesn't look like the London map will be available until early next year, so in the meantime why not take a look at some abandoned trolley images from Flickr. there's more of them up there than you might expect.
There's even a 'sad cart pool'.