If you would like to delete your account you can do so after logging in.
Navigate to the "Edit Account" page and at the bottom there is a box and a button that says "Delete Account".
Click the "remove account" button, then again when asked if you're sure.
You will be logged out, and your account and any listings you had on the site will have been deleted.
Added in How-Tos on 11th Sep 2012