Be careful with PayPal - besides all the other downsides you've alluded to, last time my old company was building an integration (admittedly, a couple of years ago) they were still using their "sandbox" environment in which you test your integration as their own personal bleeding-edge development zone - a colleague of mine spent a couple of days trying to figure out why this particular integration wasn't working, only to find out that PayPal had pushed some new experimental (and broken) code to the sandbox without telling anybody. Naturally there was outrage on their forums, but l got the impression that this happens often and that PayPal don't care. Now I will say that I have this information second-hand, through aforementioned colleague, so it might be best to take it with a pinch of salt! However, this, along with all the horror stories of small businesses/charities being put out of business due to having their funds "withheld due to suspicious activity," have led me to steer well clear of PayPal, and to encourage others to do the same!

/rant