Work related email accounts should be for exactly that purpose - i.e. work related. Therefore, a staff member should only be using a work-related email account for work-related matters.
Email observation is a good security measure, however the law in some countries stipulates that if such a policy is implemented, the staff must be notified about it prior to implementation.
I would tell staff to get their own personal account (e.g. Gmail / Hotmail / etc) for personal matters and perhaps allow a time of day in which that site would be accessible. The rest of the time is company time anyway, so only work-related emails should be handled.
My opinion, anyway.
