One thing that surprised early Oyster users on LU was that the new system knew about routes. If you live in Zone 3 and you travel to a Zone 3 station on the far side of London, you could buy a weekly paper ticket that's not valid in Zone 1, and it'd let you in (in Zone 3 it's valid) and out (in Zone 3 again, it's valid) despite your train passing straight through Zone 1. However after switching to Oyster weekly the computer would look at these journeys and go, er - no, the sane routes use Zone 1 so a ticket needs Zone 1 validity...

On day one there was no noticeable symptom. But if your Oyster only had a season ticket for outer Zones and your route was via Zone 1 the system had surcharged you, and when you tried to travel the next day the Oyster has negative balance, you can't use it until you pay off the excess. This infuriated some travellers, when in reality they had actually been cheating (presumably in most cases without realising) previously.

Today Oyster can actually track if you insist on taking the long route, you tap pink validators at key interchanges you'd need to pass through to do your slower and less central route avoiding Zone 1, and the system will go OK, fair enough, you really did go the long way so keep your money. I expect very few people do this.