PayPal has an excellent buyer protection policy, and no overdraft charges (you can't overdraft). Pretty cool for a debit card. I spend what I have, and no matter what, I can't go over.
Anyways, PayPal's "premier" account has one of the highest yields of any bank, and plus, you can't overlook the convenient of being able to pay directly through eBay. I feel MUCH safer paying through PayPal then sending a money order through the mail. Instant transaction, no extra 3-4 day wait time for the money to come through.