About 4 years ago, I used PP to transfer money from my bank account to my trading account (had done this a few times before - same bank account, same trading account). This time, after the normal 2-3 day delay, the money still didn't show in my trading account. Trading company stated they hadn't seen the funds, but the funds were gone from my bank account. Sent EMail to PP, they said to call - called, they said to send EMail - sent EMail, they said to call - called, they said to EMail; this went on/on for a couple of weeks. Their only answer was that they were 'unable to verify the validity of the funds'. They wouldn't send the funds to my trading account, nor would they refund back to my bank account. I finally had to contact my bank and have them reverse the transaction. PP had use of $1000 of my money for over 3 weeks.
Since that time, I've not used PP if there is any other way to conduct the transaction. When I sell something, and the buyer wishes to pay by CC, I send a Google-Checkout invoice. I haven't had one single problem with GC.