ISA Server 2004 Port Scan alerts

I've been running ISA Server at home for a number of years now - first with ISA 2000, and more recently ISA Server 2004 SP1. I've realised over time that there are many false alerts of port scans, and know that most times, they are false. However, there's an interesting article here which goes into a lot of detail about what can causes these alerts and how to analyse them further.