You have to pay $$$ for a money order. I don't think anybody has stated the obvious that paying someone thru PayPal is totally FREE! At the very least, if you pay with a personal check, you still have to pay for postage. And if you pay with a credit card, you don't even have to have a PayPal account!
I also really like how PayPal handles international payments by automatically figuring out exchange rates.
Then there's always the buyer's guarantee policy. On those rare occasions, payPal has never failed to recover my funds.