In the Starfleet Technical Manual, there is a throwaway detail of the LCARS user interface that when it is upgraded, users can still utilize the previous several versions. This is because their work is mission-critical and it is unacceptable to compromise the mission by forcing unfamiliar changes; eventual retraining is part of their job, but the flexibility allows them to take the retraining at their own pace.
I think about this from time-to-time and how this is still a sci-fi idea that is seen all too rarely in how we do actual computer UIs.
