I've always used norton myself. But ahve recently come into problems with it. Norton has an activation requirement, just like windows does. I've just come into problems with this now. It seems as I reformat my computer fairly regularly I've fallen foul of the number of times you can activate a particular key. Whats worse than microsoft is that rather than giving you a number to ring so that you can tell them why your installing it again etc. The only greivance path you have (as far as I could see) is to send the whole package back to them with all the orginal packaging and explaining your greivance. I personnally cannot be bothered to waste my time with it. I'll either buy a new OEM as its only £18ish online, which I have to say is unlikely because of the principle of the matter. Instead I am thinking of moving to many of the free and from what I've heard better alternatives that are freeware.
Norton is fine, but if like some of us, you do all your own maintenance and like to keep things fairly clean then you may find yourself in the same situation as me. If your unlike to bother to reformat your system or find the prospect too daunting, then you'll probably have no problem with it.
Hope that helps
Cheers
CC