I have used Pay Pal once, when it was fairly new for a purchase coming from Tim Flanagan. It worked just fine but you need to trust the vendor, because there is option to stop or question the payment as you can with a credit card purchase direct to the merchant. If you don't get what you ordered your only recourse is to deal with the seller.
When this originally posted yesterday I looked for, but was unable to find an online article about a number of law suits filed against Pay Pal by vendors that have had their accounts frozen, seemingly for no reason, and are unable to access money in their accounts, in many cases many thousands of dollars. If I remember correctly, Pay Pal has said that the accounts were frozen because it was unclear to them what the source of the money was, Fraud and money laundering being the concern. Pay Pal has little incentive however to pay it's accounts promptly regardless of whether they suspect foul play, as they collect interest on the funds they hold.
Mike