Throughout decades of growth of the world wide web, I have had to learn and use many different languages and platforms, to keep up with this fascinating, constantly evolving field.
I have also helped others to keep up - writing documentation, teaching, training and coaching. I have found that keeping people in the loop is as vital (and as much fun) as writing the code itself.
In fact, the most important thing I have learned, is the importance of human communication - amongst humans, but also between humans and computers (good user interface and user experience, clear and readable code - I subscribe to Hal Abelson's motto, “Programs must be written for people to read, and only incidentally for machines to execute.”)