I've seen many people wasting 2, 3, 4 and 5 hours of their 8 hours shift browsing those. If you will do that at work, then what did you left for yourself later at home?

That is why, we do block those whenever we will go [Facebook, Friendster, Meebo, Orkut, etc ...] not to mention all messengers and web based mails too.

Do not dwell in the past, do not dream of the future, concentrate the mind on the present moment. (Gautama Buddha)