Ok, so I also use windows....(OMG)
On my gaming machine (the PS4 posted somewhere in the forum and some pics in my gallery (
www.luisantunes.pt/en/galeria/?g2_itemId=5398 )I don't have anything virus related stuff, takes up frames and loading speeds, and is very noticeable.
On my xp laptop with a 5 year old install, I use Norton corporate 10 (OOOLLLLLD) but works and doesn't hog the machine, but then again, I only use my laptop (where I'm writing now) to manage my unixes and surf the web on known harmless sites whith chrome and ff.
For download testing, torrentz/emule and virus isolations and other weird stuff I do, I use disposable virtual machines.
The main work mule at home, uses fedora.