Doug, if the just want to track information then tabs on the employee master record is a way to go. If however, you want the system to act on that data, then your also talking about writing reports, building alerts, creating workflows, and opening up the employee master to supervisors, etc. I recommend getting a over all plan as to where you want to go with this before you begin customizing. A little is a good thing, but more is not always better.
If you have questions, I can connect you with my team and they can help give you some ideas.