I have somewhere between 7-10 (I forget as well sometimes because no problems). Different size networks (5-25 users), different load levels, different functions (email w/spam & antivirus, web, file, database, and of course router/firewall) and all perform flawlessly. I have plans for several others as well.
I've only had one crash, and that was a motherboard problem.
All the others are rock solid.