Anyway, these Oyster Cards are all very well, but they're only any use if you live there, or work or visit frequently; if you just visit from time to time you have to either go down to the Tube station (at midnight) to get a £6-something travelcard, since Mayor Boris seems to have scrapped the useful Bus pass; that or pay £1.30 for a couple of stops on a Bus; and then you can't just hop on the first bus that comes along, oh now, you have to get a Ticket from a machine on the pavement, since that's so much quicker, more convenient and more efficient.
I think getting rid of the bus pass was a bad move but there's still the bus-only cap on Oyster - and if you're getting a £6 traevlcard instead you'd only need to do it a couple fo times before Oyster was cheaper.
I think Oyster is generally only not worth getting if you're only staying a day (perhaps 2) and you're never coming back.
Getting a ticket from a machine on the pavement is quicker, more convenient and more efficient for the people already on the bus so they don't have to wait for you and the driver to perform a cash transaction. You can pay on the bus outside Central London but most people don't try to as they'd rather have the cheaper fares.