I'm stunned that someone spent time and money coming up with an index for Facebook addiction - not because Facebook can't be a problem, but because the signs see a little obvious - but the University of Bergen came up with a scale, which consists of giving a score to each of these six attributes from 1 (very rarely) to 5 (very often):
You spend a lot of time thinking about Facebook or plan use of Facebook
You feel an urge to use Facebook more and more
You use Facebook in order to forget about personal problems
You have tried to cut down on the use of Facebook without success
You become restless or troubled if you are prohibited from using Facebook
You use Facebook so much that it has had a negative impact on your job/studies.
If you score four or more of those with a four or five, it might be time to turn the computer off.