According to the Guardian the bloke behind ACS law, the people who sent out thousands of letters demanding payment for alleged copyright infringement, has given up  http://www.guardian.co.uk/technology/2011/jan/25/acslaw-ceases-filesharing-claims

This criminal was quite happy to send out threats to thousands, but when as a result verbal threats are made against him he goes off wanting his mummy. No sympathy for him.

Instead of inflitrating climate campaigners the police should have been infiltrating his firm.