I know this is probably a non-answerable question, but I was wondering if there's a way, other than say Google Analytics, to understand whether an ontology (or vocabulary) is being used... in other RDF resources (RDFa, Turtle, etc.).
For example my team maintains http://www.cropontology.org/ and it's really hard for us to get some sense of who's using our ontology and how valuable it is.
Any help or ideas?
In terms of number of triples using your vocabulary terms, one such service is vocab.cc. It's a little bit buggy but it gives counts of triples using a given class or property term from large crawls of Web data. AFAIK, the statistics aren't changed very often, but it's a good indication of the adoption of top vocabularies.
Another option is to browse through the Analytics feature of sindice.com. They are continuously updating their data, but what precisely their coverage is in terms of statistics, I do not know.
In terms of vocabularies building upon or extending your terms, checking out Mondeca's Linked Open Vocabularies (LOV) site is always a good idea. If you search for a term, you can also find out statistics on usage.