How many weeks of not playing do you give a neighbor the boot?

I give people the benefit of doubt and let them linger for 8 weeks unless I'm hurting for event collecting. If I have around 15 people not around for over a week into an event I will clean up and post in the add me thread to replenish. You can usually tell how long they have been gone by what is going on in their SF. If they have a building under construction for weeks on end for example. There are a number of other similar indicators that they haven't been around for a long time.