You may do so, but unfortunately theres alot who dont do their work because of the net, ruining for everyone.
In saying that, if people have individual logins then they should just block the sites on the logins of those who are abusing their internet usage. People who get their work done should be free to look up what they want. (within reason lol)

I am close to locking out certain sites at work because while a few do their job and I know they use the net (I dont care that they do, long as the work gets done) but there are a few that abuse it and not enough work gets completed and that shits me.
Funny thing is though, they seem to think they have a right to spend so much time on the internet when questioned about it.