There's an additional problem using PayPal for first class mail, too. There was a thread a month or two ago on The Chip Board about this. Because PayPal automatically adds delivery confirmation, you have to make sure the package is at least 3/4 inches thick or the post office can deliver the item as "postage due" and charge your receipient the Priority Mail rate.

For that reason, you are better off avoiding PayPal for small packets like chips.