I reckon 15-20% of mine pay online and the rest send payment via S.A.E. I reckon I havent collected in nearly 3 years.
I do get the odd offender who sends payment when they feel like it, BUT they do always pay and its only a couple of customers as I say, so I can handle that.
Saying that every now and then I notice that a customer has started to pay online, so I expect more customers will eventually pay this way. I dont imagine it will ever be 100% though.