I too have been using PC-Cillin for a long time. Mine is only on a few computers used by me and other family members. I have been happy with it until recently. After installing 2007 I had problems which I was able to resolve with the help of Trend Micro. After installing 2008 I have been having more problems and am trying to get help. As with most programs each new version tries to take over more of the computer. So far, among other problems, PC-Cillin tells me that I can’t run other programs that I have been running for years.
This is why I do not like all-in-wonder programs, preferring to use individual programs for AV/AT/AS/Firewall. It is much easier to diagnose issues if the services are not monolithic.
Furthermore, Most of the services provided by these programs need not run all the time- AV and firewall, surely, but for most folks, the rest is superfluous. Not only does this cause the program to be inordinately invasive, stretching it's tentacles deep into every aspect of the OS, It is also, by it's nature, very heavy on resources.