Companies will never succeed in eliminating all distractions. They can block all the sites and the employee will find new ones. They can remove the web browser and the employee will play minesweeper. They can lock the employee out of the computer, it still won't stop them from playing angry birds on their phone.

I think companies need to focus more on motivating employees to work, measuring real performance and less on counting minutes. The employee may already be obligated to work by being paid and maybe the company shouldn't need to provide any more motivation but good luck getting ungrateful employees to see it that way.