I am not OP but i use win 8 for my primary OS too and i don't use any AV. IIRC, win8 had some built-in virus protection. Also my usage is primarily pro and don't use thumb drives etc on my workstation. Also my internet habits and chrome protect me from internet side of things.

windows 8 has microsoft security essentials already installed (they call it windows defender)

Hi! I use the built in Windows Defender since it does AV now. I don't see the point in slapping on another layer of protection since I don't tend to visit dodgy sites anyway.