Vista SP1's most welcome changes should be a loosening of Vista's strict anti-piracy defenses, as I'd outlined before. They also incorporate patches delivered in earlier, smaller updates, making them the only semi-convenient way to get an unpatched Windows machine up to speed with a single download. They both fix existing bugs and add significant new features. In the Windows food chain, 'service packs' are the most important releases outside of entirely new versions of Windows. Microsoft shipped the first big update to Windows Vista today, Windows Vista Service Pack 1.
