I've never understood blocking social networking websites from employees (unless it's pornographic). If an employee is spending a majority of their working hours on Facebook, don't block Facebook. Find a better, more inspired, person for the job. Figure out how to motivate that person. See if their Facebook network could provide some sales leads. Or, perhaps, fire them.
Under-talented and over-protective
police managers help make large corporations absolutely blood curdling to work for. I'm sure it's 100% legal for employers to restict network access, but I'd argue that it's also 100% un-American. If I wanted my internet freedoms restricted I'd either move to North Korea or back in with my parents.