Not sure what all this is about really.. I accept PPPay on just about all of my auctions, if someone pays me using PPPay I use the balance to pay for other stuff (only on eBid, because nowhere else accepts PPPay), and I won't send an item until the buyer has completed the penny check (otherwise they most likely just wouldn't bother and I'd never see the funds clear to my account). This is the same way that I use PayPal - I do not have a bank account or card linked to it so I can only spend what's in the account, I prefer it that way (no way a scammer can clear out my non-existent bank account through PayPal!) I maintain a minimum balance in both (a few quid at most, usually just a few pence) as I'd rather put the money to use than have it sitting in someone else's bank account.
I think this comes down to how we want to use online payment facilities rather than individual offerings; PayPal and PPPay use basically the same principle, not my preference I have to say; on Amazon I just use my debit card, no messing, and if they can do it then perhaps eBid can organise a similar system that all sellers can use.
Faced with a choice I think buyers are far more likely to use PayPal or Google Checkout than PPPay, for the simple reason that PPPay simply does not exist outside of eBid, nowhere that I know of accepts it, probably because it hasn't been promoted at all and has no real benefits over the competition as far as the average buyer is concerned. By contrast Google Checkout is accepted by numerous different online retailers, I have used it to buy all sorts of things and there is no worry about a balance sitting around doing nothing, transfers to my bank are automatic and do not cost the earth.