The most requested features of taginfo is a view showing historical use of tags. I never had the time to add this, but fortunately there is now a solution: Martin Raifer created a service that shows the history of tags in nice graphs. You can see it at taghistory.raifer.tech. Some more background in a diary entry from Martin. Matthijs Melissen has already used this to find some interesting statistics.
Tags: openstreetmap · taginfo