IW lists the features: "A feature called network access protection that's borrowed from the newer Windows Vista operating system. NAP automatically validates a computer's health, ensuring that it's free of bugs and viruses before allowing it access to a network. Windows XP SP3 also includes improved "black hole" router detection -- a feature that automatically detects routers that are silently discarding packets."
What's perhaps most important for users to know is that if users don't want to receive the latest service pack, they need to download a tool to prevent it from installing automatically.
According to PC World, Microsoft postponed the release of XP SP3 in April because it "found a compatibility bug between the OS and the company's Retail Management System (RMS) point-of-sale software. It also stopped the automatic installation of Windows Vista SP1, which had already been pushed to some users."
"A few weeks later, Microsoft added a filter to WU to block AMD-powered PCs susceptible to an "endless reboot" problem from seeing Windows XP SP3 as an available update. In late June, Microsoft crafted a fix and added it to the WU list. Users who had WU set to automatically grab and install updates presumably have this patch already in place."
Theoretically this is the last service pack for XP ï¿¼the OS was officially retired last week.