I monitor our office network 24/7 either directly or indirectly with alerts to my company phone. I made an acquisition for a phone to be used specifically for when I am away from other resources. I refuse to use my own phone or other devices on the business network, and also have setup protocols to keep the employees devices off the network. Any Facebook or Yahoo etc. etc. time is recorded as far as when who and how often, I do not capture the key strokes and the like unless there is repeated offenses monitored. Sort of that, its a Medical facility that the employees have no business using the network as a private gateway to their own personal uses. They are allowed to keep their phones with them, with the ringers off in case of incoming emergencies and the like.
As mentioned already, if the measures are communicated to the employees then there is no problem at all. But if the company monitors without to inform the employees then it is violating of privacy and actually an act of mistrust! Also to apply special measures to a particular employee is a violation of privacy. For instance to apply a key logger to one particular client to monitor one special employee. In Germany we have strong privacy protective laws. And there can be conflicts. For instance nobody must read my e-mails at the company, but private e-mails are not allowed. I had to sign a paper at the company where I agreed with all the measures and rules.
It's personal decisions! If you wanna monitor, just do it. Like my boss, he installed EaseMon employee monitoring software ( easemon.com )on our Mac and didn't tell us firstly, just because he wants to monitor us!