Some MUDs have you register an email address when you create a character. There are quite a few reasons to do this, such as maybe having a password recovery system, or a way to link an email address to characters in case you need to restore them (say you took a 2 year hiatus). This just generally asks for an email address to go on file that gets associated with the account. If a character's password gets hacked, it could be a means for the staff to verify information about that character. I suppose something like this might also allow for you to do something like skip a mandatory newbie school session if you create multiple characters all linked to one 'established' email addy.
I have seen some MUDs that go even further with it, having you complete an in-game registration to unlock certain features (like the ability to see swearing on open channels or to enter certain zones if they are themed as being 'too adult' perhaps). This registration also gets put toward your player file is a good deal more detailed - things like first name, last name, country, birthday, gender and age.
What are your thoughts on this? Does either seem too intrusive? Would having one or both be seen as a deterrent for you? I know some of the MUDs out there some of our other players play on do both of the above - did it give you pause or not?