I run Norton ISS on all machines except a new one that came with McAfee. I have had ZERO problems with Norton other than an occasional 'warning' that is bothersome on new files d/l'ed, but I'd rather have that then just allowing them to run, it makes me think about it. McAfee on a new computer that is faster than any other here seems to have more of a load with it than Norton does.
I agree that years ago Norton was a 'load factor'. With today's systems you never know it is doing anything, however, I suspect if it were not there the system might run faster. Don't forget, a suite, like Norton's ISS is not just an A/V but a complete configurable Firewall as well, and if you want more there are other features like Parental Controls and a Date Safe, and more.
Like WHS, I get mine basically free on Black Friday sales, so I don't care to switch. Even then, the price, usually on sale for about $50 isn't bad for a year on up to 3 PC's.
P.S., not solving anything, just stating the facts as I see it.