Norton has a really bad reputation because most people that have used it remember it from the days it basically raped your Microsoft ME's 256mb of RAM and a processor that was today's equivalent of a small Asian child with an abacus.
Today, it is vastly improved and receives almost universally positive reviews.
When I still used Norton (Around a year ago) it bothered me 24/7, and interrupted my games like crazy.
It hogs my RAM and runs scans at the worst times when I'm playing TF2 or CS:S.
Then again, that was a year ago. Who knows.
I love Avast! though.