I've been using Kaspersky for years and never had a problem. At the moment my two laptops and netbook have Kaspersky Internet Security (2 year 3 computer license) installed and the desktop is running Kaspersky Pure 2010. Both programs update their databases and scan the hard-drives automatically using little processor power and are unobtrusive, even on the netbook. I've also found moving my license from one computer to another is a snack.
Another aspect that deserves praise is Kasperky's helpdesk. I'm not sure how long I've been using this product but it must be more than a decade and, in this time, have only had to ring them regarding proceedure, not problems. Each time my call was answered immediately and the person I spoke to gave the impression they were experts, not someone reading from a process cue card.
Every now and then I'm asked to recommend an antivirus program and, without hesitation, I suggest Kaspersky but, invariabley, this advice is ignored and the enquirer opts for something free off the internet. The next I hear about it is the person whinging about not having their computer for a couple weeks while the local computer shop removes the viruses, trojans and malware then charges three times the cost of Kaspersky for the service.