An idea I am presently working on is building a simple Drupal site to provide a controlled vocabulary to other Drupal sites as well as non-Drupal applications in D7.
I'm curious if anyone has tried to do something like this at some reasonable scale? How many terms were you able to support? Did you use the Services module to make the terms available for use in other sites? What method of term ingest did you use? Did you include definitions or synonyms? Any additional thoughts or warnings?