I received this e-mail today:
You have not logged into your account in over four months. As a matter of CouchSurfing Project policy, we simply deactivate accounts that haven't been logged in to recently.
You can fix this though! All you have to do is log in and your account will be active again! To continue your account, just log in: http://www.couchsurfing.org/login.html
The CouchSurfing Team
You should consider implementing this policy. It would remove the dead wood, give you accurate member counts and encourage old members to return.