I've made a patch for support for hiding category/taxonomy input fields.
This is useful if you are building your own plugin and want to store custom meta data for categories serialized in text fields, but don't want the user to be able to manually modify it. (The other solution (that would be harder to debug), but also suite my needs is to make it possible for other plugins to add custom field types and with callbacks to them.)
It can be downloaded from: http://gw.tnode.com/0275-WordPress/
Feel free to include it in the official version. If you decide to write credits, just write "GW <http://gw.tnode.com/>".
P.S.: It would be nice if there would be an email address or some other metod for posting patches described in the readmes or on the page. Maybe just allow opening of Trac tickets by anyone or sth..