I'm not REALLY sure if this is a bug or a feature request.

user warning: Duplicate entry '0-73' for key 1 query: INSERT INTO term_node (nid, vid, tid) VALUES (73, 73, 0) in /var/www/htdocs/LBH/modules/taxonomy/taxonomy.module on line 716.

I want to keep a 'source of business' list quite short, but allow people the option of choosing 'other' so that we can record where our business is coming from.
It's unlikely that I will often add any of these 'other' entries into the list as the fact that they are not already there means that we do not actively advertise in that way BUT, it's possible (even likely, eventually) that more than one user will type the same thing in the other box.
I want the user added options hidden, but equally I do want new users to be able to type in that option without causing an error. I could hide the error but I want that users account to be created with that taxonomy option selected so that I know how many people have typed in that phrase.