Yes, Norton are trying to follow the Micros###e lead, by getting their product bundled with as many new PC's as possible. However, in every instance, I've found that by getting rid of it, cleaning the computer of all traces and then installing standalone AV and firewall software (normal choices are Avira for AV and Zonealarm for firewall, both industry standard products for free) the startup performance and general speed of the machine is massively improved.
I personally would never pay for anti virus software, why would you when there's so much good stuff about for free?
And as for uninstalling Norton before installing another AV product, yes, it's ABSOLUTELY necessary. If you don't then Norton will throw a major hissy fit and try and delete all the virus definitions etc. for the new product. I've seen it done as an experiment, and the computer refused to respond to ANYTHING for four whole hours, and this was a fast machine. Eventually it sorted itself out, but the installations of Norton and the new AV product were both severely damaged, and some data was lost from the hard disk!
If you download the installation files, then disconnect from the net, you can perform an uninstall of Norton, fully clean the system and install your chosen AV product in complete safety.