A reason for accepting months as words is that some people (including myself) struggle to remember the numbers of the months! Obviously, there's no equivalent problem for days, so allowing 'th' and 'nd' doesn't help anyone
Lee Crossley we avoid doing it. I believe it is bad for accessibility ( Tom Byers can confirm). It can reduce usability for users who are not expecting it. It also makes it harder to correct errors. The user need is to support people filling in the form, not filling it in *faster*.