I had made a couple of donations via PayPal and got no acknowledgement bar the automated email confirming payment.
That's exactly what I was fearing. It only came to light recently when I knew a donation had been made and was waiting for the accompanying letter to come across my desk. When I finally asked where it was I was told that there was no postal address listed with Paypal and that this had happened before. PM me with your postal address and we'll sort it out.