I'm testing the new version of gosmore with it's powerful search functionality. It tries to built an index of all the meaningful tags in the planet, like 'fuel'.
The problem is that there is so much stuff that it meaningless to the average user : The majority of it is TIGER ids which is easy to suppress. But there still a lot of nodes with class=node tags and time=... tags and ele=... tags and and and.
There are even a few ways that refer to nodes that no longer exist. (e.g. node 80169)