Currently it appears not to be possible to know, in the ajax error callback, if the request has failed due to a timeout, versus some other reason. Knowing this is important for implementation of a good UI, which wants to be able to say more than "timeout or other error". I propose having the "status" parameter contain string "timeout" when the error is due to a timeout. This seems trivial to do, fe. by the patch at http://pastebin.ca/613865
