In times past this might have been cause for alarm. I believe, though, that I can now handle this. I have had my paypal card for probably a couple of years now and have not abused it, have handled it well. I keep the balance at zero as much as I can, yet charge on it often - just pay it off frequently. I now qualify for better cards, better interest rates.
As much as anything else, I see these cards as a type of insurance. If really pushed to the wall, I would be able to pay for an emergency or a problem bill. I prefer to pay cash, as always, but it is comforting to have a backup.