Delicious is switching to a new system, and put on a tutorial for its users to maintain their account, my guess is that a large part of its users won’t return after the switch and will turn out to be ’sleeping’ users.
I remember talking to a guy who worked full-time for an ISP and did nothing else but handling dead people accounts. They kept charging these people who NEVER logged on and never complained. They had special mechanisms to ensure these people wouldn't be bothered with mail (since they were often literally dead) so they could keep charging them...
But were they really users if they're just "sleepers"? Depends how you define them - I would call them account holders.<p>In the mobile telecom industry, they use a metric of "users who made a phone call in the past 90 days" and similar for each service (SMS, internet, etc). This negates any inflation of subscriber figures from Pay as You Go kind of billing who may use a SIM card once a year.