I handle 10-20 payments daily from paypal and I use IPN to automate things. 20-30 minutes ago a payment went through. I received a payment from subscription of £11~. I received the subscr_signup IPN. Then 10 minutes after or so I received the subscr_cancelled. I checked IPN history and Paypal never sent out the subscr_payment that it sends out on all other payments. I did receive the money and it was successful but Paypal never sent it out. This gave me some mild headaches but I was able to add the records manually to the database. But it's a pretty bad experience. What if I was dealing with hundreds of even thousands of transactions day. No chance that I could deal with this happening often.