Here's a date for your diary: 15 November 2008, Junk Mail Revenge Day.
The idea for the 'Revenge Day Plot' started on Facebook [Link removed in May 2012 as it looks like the group no longer exists / has been deleted by Facebook - JB], but anyone can join in. All you need to do is collect any junk mail with a return address between now and 15 November 2008. Then, on Revenge Day, put it all back in post.
It's an interesting experiment. If everybody would return all the junk mail they are not interested in the era of 'economy of scale' marketing would soon be behind us. Unfortunately, most junk mail ends up in the (recycling) bin. This does nothing to reduce waste, to stop the destruction of ancient forests or to reduce your Council Tax bill. The Revenge Day can change all this, simply by making the sender pay.
So far I've collected three pieces of junk mail; one of those annoying 'To the Occupier' items from HSBC; an appeal from Cancer Research UK (a charity renowned for sending large amounts of junk mail) and a letter from Charles Clarke MP (who, I'm sure, can afford the return postage.