Anyone who's registered a new nickname with the web client in the past couple of days (by just using a new nickname/password combination) might have noticed that an e-mail address box then appears (without changing anything else on the form) in which you are to enter an e-mail address before logging in.
An e-mail address is now required when you register, either via the web client or via the /ns register command. We were running an unsupported hack for a while to remove this requirement, but for the sake of maintainability, it has been removed. This is a requirement of the services package we use. The e-mail address you enter won't be used or verified in any way, but it must be valid, and if you do use a real e-mail address, services administrators will better be able to assist you (for example, by resetting your password which will send the new password to you via e-mail).
We encourage any users who don't have an e-mail address set yet to set one by using the /ns set email command. After a couple months, we may start sending memos to users who have not done this yet so we can get everyone on the same page.
As always, please let me know if you have any questions, comments, or concerns!