most servers should have data loggers, not sure about the software though.
In Australia, provided you make sure the employees know that their internet use will be monitored it's not an invasion of privacy. Reading/checking their emails is another matter.
My last workplace had a glut of server traffic between 4:45 and 5pm. The IT manager closed access to the IP addy's for Ebay and Google earth.
As a business owner I'd be wondering if I need all that overhead or if I can shave some of it off and either gain some margin or lower the price of my goods/services and gain a little market share.
Staff deserve to relax if they work hard but if you can cut overheads without affecting internal and external service levels...