Microsoft might choose not to tell its enthusiasts anything about Windows Vista Service Pack 1, but they can’t afford to keep it a secret to the development community. For the same reasons some argue SP1 is the Holy Grail for Windows Vista, a newer kernel means changes to a very significant component of an operating system. However this is a significantly minor update to the kernel compared to what was endured just months ago, APIs have already been added, changed and even obsoleted.

Collection of published Vista SP1 API changes from MSDN