Maybe the cause of so many on-posters is because they registered and then either didn't choose to come back or they had no way of deregistering for whatever reason. How about a time limit for new accounts where if it's unused for a certain amount of time/posts it gets automatically deleted? And an option to delete your account could help if cleaning up after yourself is encouraged. If you aren't coming back, kill your account so we can reuse the name or something.
Cheers!
