Amazon, bless them, have let their CF algorithms get a bit wayward recently. I just received this missive:
Hello, Ian Dickinson,
We've noticed that customers who have purchased or rated Harry Potter: Years 1-4 (4 Disc Box Set) have also purchased Classic Farm & Agricultural Machinery (3 x DVD)  on DVD. For this reason, you might like to know that Classic Farm & Agricultural Machinery (3 x DVD)  will be released on 13 August 2007.
Leaving aside the small matter that people who have bought one thing by definition haven't bought another thing that hasn't been released yet, anyone human looking at the correlation between Harry Potter (I bought the DVD's for the kids, honest) and Classic Farm Machinery is going to do what I did: laugh out loud. Which makes me think that research into the understanding of humour by computers - some of which has been in the press recently - may have a purpose beyond illuminating our understanding of human behaviour. If we create computers that can get jokes, they might be better able to spot stupid errors than automatons that just follow the numbers.