I'm searching for a away to check newly added tag in tag-it (http://aehlke.github.com/tag-it) via getJSON request and allow adding tag with (eventually) edited tagName or disallow adding new tag.
For example: Entering "audi s3" will trigger beforeTagAdded event which should do the getJSON request, response from server will contain something like "Audi S3" or "Audi S3, 2007".