In the past, I have been an advocate of AVG and, until this version, had no reason not to be.
Unfortunately, it has been slowing my system down. The automatic scan, set to start at 01:00 hrs, was still running on the 160gb SATA drive at 09:00, with an 80gb IDE drive still to go. And, to add insult to injury, according to Vista's 'Performance and Maintenance - Advanced Tools', it was also taking its toll on Vista startup and shutdown.
It isn't anymore because I have uninstalled it. Until such time as I hear that it has been improved, I will be trying out Alwil's Avast 4.8 free version.