Commons works best when you use known pictures. As it says on Commons, it is "a database of 12,959,488 freely usable media files to which anyone can contribute". Anyone can and, it is becoming ever easier to contribute even more media files. The problem is not so much contributing files, it is finding them and using them. Many people I know prefer to find pictures elsewhere. I tried to find pictures of a bunch of keys on Commons for a recent blog post but after too many pictures of Alicia Keys, I gave up.
At the Berlin Hackathon 2012, it is the kind of thing that merits some shared consideration. The existing categories on Commons just do not help. When looking for keys, you want to choose from all keys and not navigate a structure. It makes more sense to have tags and possibly disambiguate those tags. Combine them with other tags and you have a result that will be more satisfying.
The value of a collection is in its use.