I lost $250 in the first instance and $100 in the second. Not crazy amounts of money, but I worked quite hard as a writer to earn it, so I was angry as you can imagine.
Another problem I've encountered with Paypal is the chargeback system. They'll always support the buyer, so unless you have proof you sent the item and they received it, the buyer will get their money back. When you sell domains, they can take the domain then ask for a chargeback via Paypal, although this only seems to happen with Godaddy.