After many (read: 7) requests for such a feature, I've added a Close Account
option to UER.
To access it, click Profile on the sidebar or here: www.uer.ca/forum_myaccount.asp
Most of the time, there is no need to close your account. But a few people like to "storm out" in a huge hissyfit, like that kid in pre-school, so now they have that option.
When your account is "closed", it means that nobody can send you messages nor can you log in.