I'm a little disppointed in NIS (since upgraded to 2009). It was completely helpless in the face of the most destructive worm, trojan, and virus I've ever had. These were: Zlob.DNSChanger.Rtk and SillyDC (the 3+ is for some additional files, tracking cookies, etc that I could find a name for).
NIS did diagnose the SillyDC problem, but it was unable to do anything about it. Multiple identifications and restarts did nothing. I had to boot to safe mode and manually remove the files.
The Zlob rootkit was never picked up by NIS at all (after it had already been foolishly installed). I had to get SpyBot S&D to even identify the problem.
It's frustrating that a free software that uses a lot less of my processing time was able to fix a serious problem then a program that I paid for and that hogs my memory. All that processing, but little help when it counted.