Specifically, does it make a perceivable slowdown? I'm asking because the only thing stopping me from buying and recommending NOD32 is the fact that I've seen it miss too many viruses, namely trojans, that KAV picks up. I've read the other threads where Eset discusses their somewhat slow response time in adding new definitions, and my understanding is that they want to keep their virus definition base "clean." So this leads me to wonder if there really is a noticeable slowdown in performance from adding virus definitions. I abosolutely love how light NOD32 runs on a system -- it's just that NOD32 doesn't make me feel safe from trojans while surfing online in its current state. If Eset's issue is slowdown, I can completely respect this as they've built a reputation as the lightest, reputable antivirus available. I just wish they'd cover more of the big trojans that their heuristics miss. If there's another reason for the smaller virus base (compared to Kaspersky and Mcafee), like Eset is more concerned with improving their heuristic engine, then I'd like to hear it. And yes, I know that good anti-trojans are available. But I end up paying more than if I had just bought KAV, and I lose NOD32's best selling point for me: lightweight, real-time protection.