Active users are probably the key to identifying fake and inactive users. There are likely to be patterns of use on Facebook from active users which apply thems

Active users are probably the key to identifying fake and inactive users. There are likely to be patterns of use on Facebook from active users which apply themselves irrespective of whether a given user is a power user, casual user, etc. Adding friends, sending messages, checking other people's walls, having other people check their wall. Anyone who doesn't conform to this pattern to within about 10% either side (not enough use / too much use) is probably a fake or spam account.