I've had this app for years and I've never found it to noticably slow down any of the Macs I've used it on which include: Mac Pro, iMac (Intel), iMac (PPC), G5, and PowerBook G4.

There was an earlier version of X5 that caused intermittent crashes on the Intel iMac when Read Time Scanning was on, but that has since been fixed, other than that, there have never been problems for me.

Last night it found its first virus too. It found a piece of Malware on my Vista drive, and it was able to repair the file. Surprisingly BitDefender didn't find it (and it's a Windows AntiVirus app), but sure enough VirusBarrier did. I'm impressed and will continue being a loyal Intego customer.