I'm using Spyware Blaster with AVG, Spybot, ZA etc. Not noticed any problems. Never notice the scanning speed as don't use the schedule scan, only manual scan and usually only kick it off before going off to do something else. Maybe it loads a bit slowly on startup, that would be my only complaint. I tried Kaspersky Internet Security on Vista but it nagged me too much. So I'm back on AVG.