We have been using ClearCenter and ClearOS for 18 months now. Prior to deploying ClearOS we had been plagued with spam, both incoming and outgoing (1.5 Million messages in one day!),to the point where our ISP was going to terminate our connection to their mail servers and no more mail. I removed all network connections (50+ pcs) in the office over a weekend and began rebuilding the network using a ClearOS firewall to monitor network traffic, check for viruses, scan for spam, filter out ads and generally split the network out into set groups with no shared relationship.
System setup took less than half an hour. A little more to time then to fine tune the system, block bit-torrents etc.
It has been a real admin delight to set this up and let the system do its thing and only occasionally check reports on domains and pcs that consume the most bandwidth.
I have add egroupware to the server for resource tracking and wiki, etc. The system is used for file sharing both internal and FTP when employees are out and about and need files there and then.
This is the best SME server, firewall, gateway system you can get.