Is facebook a time waster....

If we look with a systems perspective the processes and the data flow between the processes should be very important.
In this case we do not know much about the processes in the system so it is very difficult to answer such questions (they may be biased).
The effect of facebook will be different for different types of organizations as most of the organizations have different processes.

If we take an example of a recruitment company which headhunts candidates and places them in different organizations. Then the boundaries and environment are more clear.

do you think that facebook is a waste of time for employees?
It would be a great tool for finding prospective candidates, there would be a lot of false profiles , but screening is the job of the recruitment consultant (interviews, questionnaires etc). We can take the example of many credit companies, In Australia organizations are hiring people to go through facebook and other social networking profiles to find out the bad creditors who have gone hiding. Even police are using facebook for finding out more about criminals.

What are the benefits the company gets?
Again, this depends on the processes of the company. In the recruitment consultant scenario the benefit would be more prospective candidates.

What are the benefits the employees gets?
Facebook will make the employees more motivated. If we take into account the Maslows need hierarchy the social needs of an individual are quite important, hence it is important for the employess.

In conclusion , facebook would be great if used in a proper way to attain the goals of organization. Facebook makes it very easy to detour but it is the job of a good employee to be in line and on goal.
The onus remains on the HR department of the organization to select and retain a perfect employee for the organizations need.