I have a large taxonomy (and about to grow a lot larger) with several thousand terms in it. When I'm editing a post, there is now a significant hang when it goes to load the term list.
Has anyone run into this before? Any suggestions for dealing with such a large list?
This is probably because your taxonomy is hierarchical, and the default meta box for such taxonomies is similar to the category box - which displays all terms as input elements. So the browser lag for thousands of elements within a page is expected in this case.
If you can't make your taxonomy non-hierarchical, try removing the default meta box and create your own, in which you display only the most used terms, a single input field with autocomplete or something similar
