I have never worked for a company that did not allow a bit of personal business - checking in with family, making phone calls that can't be made after hours, life business - to be done during the work day. There is rarely a zero-tolerance on such things, and if there isn't a zero tolerance policy, an employer would be best to not eavesdrop with things such as keystroke trackers.
If the usage of the computer for other-than-business gets out of hand, it will show up in other ways. The affect on morale of feeling that big brother is watching and listening, is worse than a few emails.