There's been a some questions on this board lately about the final release of SP2. For those of you who use XP, you should take a look at this news article by Scot and decided for yourself whether you want to take the plunge or not. It also explains in detail how MS plans on releasing the SP to the general public.
As I understand it, the main thrust of the update is aimed at computer users who have poor security measures, i.e. not running a firewall, not using an AV software etc. That doesn't necessarily mean that those of who do have such protection shouldn't update to SP2. But if you are, then I would agree with Scot's advice of waiting for a while before updating since the urgency isn't as great.