I just recently launched PS3 and I am running PayPal Express. I put in a purchase, it took me to paypal and I put in all the information and was taken to the transaction success page. The purchase is showing up in the admin area. I did not receive a receipt (email) and the store did not receive a notice of a purchase. The payment did not go through Paypal and I do not have Sandbox checked. One thing that I did notice is that the payees information was not added to their account on the site. I had to go in and manually add my Name, address, email address and other details.
If this is the same problem that Sheila was having I would like to see the resolution to the issue.