We've looked at this, but we've decided against it for now as we don't actually want anyone booking without speaking to us first. That way we can decide if they are "suitable" or not
The paypal discount is attractive but we only have about 5% of our bookings paid on paypal anyway - and that's nearly always because they are foreign, and we just use paypal to get around the currency issues. Most of our UK guests are perfectly happy to pay by bank transfer so it's a bit of a red herring really.