I've been extremely impressed with the Oyster user experience thus far. I travel on tube or bus in London relatively infrequently and variably - I walk to work, so it's really only random journeys from Broadcasting House to Bush House, and then a regular once a week to play football in Kennington Park. That's it, apart from ad hoc journeys at weekends. Nowhere near enough to justify buying a travelcard, so the new pre-pay Oyster card is ideal - it's more convenient than fumbling for change, and it's cheaper (journeys are at 2003 prices).
It was easy to obtain (fill in a form, take it to the local tube), and I've just recharged the card online at the excellent Oyster website. The login process was simple (unique ID printed on card), the shopping cart relatively straightforward and essentially 'good pattern'-based, and the website design - being clean, simple, professional and modern - inspired confidence and quickly began to engender trust. Don't know who's behind it, but good job.
I know this sounds like an advert (and am aware of concerns about tracking journeys), but due to the size, complexity, and lack of coordination within London, I'd pretty much lost all hope of the city's transport infrastructure being significantly improved. Yet Oyster is really very very impressive, and part of a suite of massive improvements by Transport For London/Mayor of London in the last couple of years (alongside new buses & tubes, better signage, the congestion charge etc. - albeit a potential minus with the bus ticket machines). So, still work to do but nice one, Ken + team.