I have un-installed my old Norton as it expired and it looked to be quite expensive to renew it, but when I signed in today the Norton Pc check came on. I don't how it can do that if Norton has been uninstalled. As you say bits of it must stay behind. I used the Norton removal tool.
It does seem that even the Norton removal does leave some things behind. When i cleaned out my Internet Security 2009 and installed Internet Security 2010 from CD it found the old scheduled scan setup that I had been using.
No other problems that are obvious though.
Had a problem renewing norton couldn't get it in ,Got intouch with norton who put me through to one of there indian chaps who did the job while I just sat there and when he'd finished he gave me an extra 25 days you can't beat that for service