I don,t have an anti virus program running resident on my Windows 7 installation. As I wipe it quite often and replace it with a safe image, or a new build, it doen't seem too important.
However, I think, for the purposes of testing, I have installed and deleted Anti virus programs faster than new buids have come out!
They all gave, unimportant, a desktop delay penalty on startup. I would say, on my own observation, Avast was the worst here. Generally, they all seemed to perform unobtrusively. Nod32 may have had the edge.
The biggest disappointment was my favourite - AVGFree. Heavy on resources and in general internet procedures.
Maybe when everyone catches up with modified programs for 7, the whole benchmark scene will change. So the jury is still out for me.
P:S. I did not include ANY Norton products. That has been a no no for me since Vista started. Shame on them. Peter Norton was one of my Computer heroes in the Dos days.