I once saw an account of a guy, wich the last time that he signed in was in 2009.
And he had no forum posts.
But he posted 2 or 3 tabs.
I think that accounts like that sould be kept, just for the tabs, but those guys that don't sign in for a year, and don't post on forums, and only use their accounts to "add favorites" should be deleted due to inactivity...
In fact, it could be a good idea. When you create an account there could be a special warning that says
" WARNING (
) Account will be deleted if user's period of inactivity is bigger than 12 months (or so)." and you could e-mail the people either warning them that their account would be deleted or just saying that their account is already deleted. Most people wouldn't even care, since they havn't logged in for a year.
That's my suggestion.