I have been using Avast (4 & now 5) and ZA Free and later ZA Pro for over 3 years now. I started out with Avast 4.8, ZA Free and XP. Later while still using XP, I upgraded to ZA Pro. Then last year I bought a new Dell computer with Vista. On this PC, I started out with Avast 4.8 and ZA Pro. I later upgraded to Avast 5. In all this time I never had a BSOD caused by Avast or ZA. I have had serveral minor problems that were quickly resolved by each software tech reps or thru their forums.
regards
johnb
Vista Home Premium, SP2, 64Bit, Dell 435T, 6GB RAM, WD 1.5 TB External HD, IE8, Avast Antivirus 5.0, Spybot S&D, ZoneAlarmPro, Malwarebytes' Anti-Malware, Windows Defender, Windows Malicious Software Removal, SuperAntiSpyware, Spyware Blaster, cCleaner, Glary Utilities, Speccy and Dialup.