I have been looking for a software like this for quite some time for my wife. She spends too much time on Facebook, and I always want to quantify that time so that she realizes what a waste of time it is.
And someone has finally made a software that does just that. Facebook Runner is a free browser extension that does just one thing: It tells you how much time you spend on Facebook. It automatically starts working when you are browsing Facebook, and you can access it at any time to see how much time you have spent on Facebook.
This browser extension does not needs any configuration: Just install it, and it will start working.
Facebook Runner extension is available for Google Chrome, Firefox, Opera, and Safari. Surprisingly, developer has not done anything for IE yet (a toolbar?).
If you are a big fan of Facebook, but do not think you spend lot of time on that, do try out this extension. You might be surprised how much time you are spending on Facebook. Download Facebook Runner here.