I have one Windows box left on my network (running XP Pro). As long as you are running a good Windows based firewall (Norton Internet Security Professional does it for me), and are using a decent browser (Firefox 0.92 in my case), then there is no point upgrading to SP2 whatsoever.
As Neo says, if you are an experienced user, you'll be looking after your system properly anyway, and won't need Redmonds "help"!!