http://news.bbc.co.uk/1/hi/england/h...re/8231234.stm

A council is to ban Facebook on its computers after it was revealed staff spent on average 400 hours on the site every month.

....

each of its 4,500 staff .... spending about six minutes a month on the site.
I don't like or use Facebook. But what exactly do these people expect to gain from blocking Facebook? An extra 20 seconds of work off each employee every day?

I guess that they have not considered that staff are now going to be leaving work earlier or returning from lunch break later as they take their work laptops to the nearest Wifi zone or go for lunch in their nearest Internet Cafe.