10-14-09 - Paypal is having problems with IPN - which will affect anyone who has a zen cart using paypal as a payment method. You can see the information here:

http://www.pdncommunity.com/t5/Live-Site-Status/Live-Site-945-2-Update-Instant-Payment-Notifications-IPN-is/ba-p/158035

One suggestion was to turn debug mode ON to see if you will get the order information through a debug email. To do this, go into your zen cart admin area, mouse over Modules >Payment. Click on the paypal link and click to edit it - the debug email option is at the bottom of the page on the right.