Once upon a time, Norton Anti-virus reigned supreme in the anti-virus world. Fast, easy to install, small footprint. Unfortunately, that was in the year 2000.
Since then Norton has become the exact opposite of all that. Now it's slow, often difficult to install -- and especially uninstall -- without side effects, and the program has far surpassed the level of bloatware.
To top it all off, Norton appears to miss a LOT of viruses and is very slow to update. Poor Peter Norton's legacy has befallen the bureacracy of large scale companies.
Personally, I am recommending a couple of other alternatives to Norton.
For free antivirus software the last holdout seems to be avast. http://www.avast.com. It catches a reasonable amount of viruses, updates fairly often, has a relatively small footprint, and the price is right.
For paid antivirus I feel Kaspersky is now king of the hill. It consistently ranks high in the best antivirus detection as well as update speed tests.
Now if you currently have Norton (or McAfee for that matter) I would continue to use it as long as you're happy with the results. However, if you find that your computer is running particulary slow when you check your Outlook email or if you are still getting a fair share of viruses on your system, then consider switching over to Kaspersky http://www.kaspersky.com once your current subscription expires.