Pre paid Oyster Cards let you charge them up with money, and then spend that money on train and bus travel. It sounds like a good idea, and could be the basis for e-cash in general (Oyster could sell or rent machines to small retailers, in much the same way that Visa does).
I want nothing to do with it, and I'm saddened (but not surprised) by its acceptance.
Here's how Oyster works as a metaphor with normal cash :
You hand your wallet over to the bus driver, he takes out some money without you being able to see, and then hands you back your wallet. You can't immediately check how much he's taken, but you could do at a later date (but nobody ever does).
If he's taken too much, tough, because he's incapable of giving refunds. If you want a refund, you have to spend much time an effort battling the red tape and help desk monkeys.
You have no proof of purchase, and if an inspector says you haven't paid, you have no way to prove that you did.
You don't own your wallet (despite paying £3 for it), and must hand it over to officials whenever they ask for it. If they feel like it, they can keep hold of it, and if you want your money back, you have to go through the more red tape, and those help-desk monkeys.
If you think this is overly alarmist, think again. A friend of mine has had her oyster card taken from her (including the cash on it of course). She had to spend hours on the phone to get her money back. (The ticket inspector claimed she hadn't swiped her card, and after many phone calls Oyster admitted that it was their fault, and she had done nothing wrong).
There is also two example of 'theft' using e-cash. The first is with the Oyster card. There are journeys you can take which Oyster believes are through zones 1 and 2, but are actually only through zone 2, and therefore you are charged too much. You'll never notice because the money is silently removed from your card.
My second example of e-cash 'theft' happened to me using another e-cash card (operated in my place of work). This card is slightly better than Oyster - it never removes money silently, but I still got ripped off. I stuck my card into the vending machine, selected my snack labelled as £0.60. It told me it had charged me £1.00, and gave me my card back. With these vending machines you have to put your card in before you select an item, and there is no confirmation step, so there was no way I could stop it from overcharging me.
I don't want an Oyster card, if I get one, then I'm admitting that I'm knowingly, and voluntarily participating in something that can con me.
It never used to be a problem, I bought books of tickets which were only slightly more expensive than the Oyster prices, but they stopped selling those. I can still buy tickets from the driver, but these are outrageously expensive, so I hardly ever do that (over twice the price of Oyster last time I checked).
So now I use cars more often (my mum's) (bad for the environment), and I also walk and cycle more (good for me).
How e-cash Should Work
Its not hard to work out how e-cash should work, it should work exactly the same of ordinary cash.
You take your goods to the till. The till shows you how much to pay. If you are happy, you take that much money out of your wallet and give it to the the teller. Simple.
Translating that into e-cash.
You take your goods to the till. The till shows you how much to pay. If you are happy, you attach or swipe your electronic gizzmo, and press a button on you gizzmo to confirm that the money can be take out of your gizzmo and put into the till.
Its important to note that the electronic gizzmo isn't a passive device. It has a screen and a confirmation button. Without these you are putting your trust in the till. I could make a till that showed £0.60 and charged you £100.00 (a regular till showing £100.00, an extra lcd display showing £0.60 and some double sided sticky tape!). Too expensive to have a screen and a button on the gizzmo? Nah, it just a calculator, and they cost about the same as an oyster card. What's more, banks are now giving away gizzmos for on-line banking, which could be redesigned to work as e-cash too. http://www.nationwide.co.uk/rca/Introduction/why.htm