I answered this one a couple of weeks ago. We have started removing accounts that have never been used and are older than 15 days. So it is only the accounts that signed up didn't even do one free roll and never came back.
OK, makes sense. But are such accounts deleted completely, or only removed from referred users lists? ie. what if someone, with such account, tried to log-in after 15 days after all? Will they be able to, or will they be asked to create new credentials?
Sorry if this has already been answered, this thread is bit too massive to be scanning through it.