Is Facebook/Twitter a waste of everybody’s time or could companies perhaps benefit from it?

It is becoming an obsessive trend amongst some companies to close people's access to Facebook at work. It is true that people spend a lot of time on Facebook or Twitter while they are at work and thus while they are supposed to be doing something else - work. But is it all bad?
From the companies perspective there cannot be a good argument for "Facebook time" while people are supposed to be working. The current statistics show that traffic on Facebook during work hours is enormous. So the social media giant is attracting a lot of people socializing while working. Can this go hand in hand? According to some companies in the financial industry, it cannot. The management team of some companies in the financial sector is so annoyed by their Facebook visiting workers that they have decided to completely close access to Facebook from work.
But is it true, that people are wasting time on Facebook? It is true that a lot of people go online and go on Facebook. It is also true that it is perhaps not directly a work related activity per se. Posting about what you are having for lunch or how hard your work-out was this morning at the gym, is hardly contributing to what we would call "work". But should companies be concerned with this?
Some are obviously concerned that time is being wasted. However, studies have shown that people who use social media such as Facebook and Twitter while at work tend to more productive. A study carried out at the University of Melbourne discovered that people using the web for personal surfing get more work done than those who do not. The study was carried out by Dr Brent Coker:

"People who do surf the internet for fun at work - within a reasonable limit of less than 20% of their total time in the office - are more productive by about 9% than those who don't."

Dr Coker states that most projects, such as writing a report, consist of mini-tasks such as researching information, entering data, creating a graph, etc. Workers were shown to take small web-surfing "treats" between these mini-tasks. That enabled the mind to rest itself, leading to a higher total net concentration and increased productivity.
Work breaks are not a new thing. Smokers today need longer breaks every hour now that they need to go out for a smoke.
So why not just let them relax a little and go online, for fun?
The bad news is that most of the companies' customers are probably on Facebook and Twitter as well. So any talk about the company is going on - the company is simply selecting to ignore the discussion that is taking place about the company's products and services in these media. Ignoring this "talk" can be dangerous to the image of that company.
Let's take for example Icelandair. During the eruption of Eyjafjallajokull, most air traffic stood still over Europe. People were not getting to the places they wanted to go to. Some blamed the airline companies, airing their anger on Twitter. Icelandair was monitoring the discussions that involved its name. That way they could correct any misunderstandings that were being stated.
But another remarkable thing happened as well. Happy customers of Icelandair were also taking part in the discussion correcting anything the appeared to be wrongful statements, according to their own experience. All this was very positive for Icelandair, who stood to lose a great deal of customers, money and not to mention damages to its image. Their Twitter service was excellent during the eruption. They usually launched updates on Twitter and Facebook offering people who were online a more direct and personal communication.
So not only is it wrong that people wasting time on Facebook is bad for the company, many companies need to completely change their opinions on social media in general and learn how they can benefit from it rather than ignoring it.