Trend Micro SmartSuite - We run this at work and LOVE IT. There was a major issue in May of 2005 regarding a bad virus definition causing havoc. I need to get the details, we were not affected. I think Trend changed their problem resolution procedures and addressed this. All antivirus products will have these occurrences, its how the manufacturer changes in response to the incident (or ignores it) that counts. It's all about risk management - do you risk not running antivirus or updating infrequently? Not me, we update hourly and have not had a virus infection since 2000.

Sybari Antigen - we run this product on a dedicated SMTP server. It is pretty nice in that it can quarantine all compressed archive files and then we release them when needed. This philosophy has stopped a few viruses from entering our mailserver.