Actually I forgot about the quantity of users available via server manager - great point. In thinking about this again, I realize that from Security Audit Reporting, you actually can get the names of all users who have logged on.
So - best of both worlds:
- Use Server Status to see how many are on right now
- Use Security Audit Reporting (can get to AUDITRECORD table directly or thru a query builder report if desired) in order to see actual users who have logged on.