After denying the existence of service pack for months, Microsoft has confirmed the release of SP1 in Q1 2008.
This pack will make windows more reliable, using error-reporting data to determine the “highest-impact” issues, says David Zipkin, a Microsoft senior product manager.
This release is expected to boost adoption rate of the OS by corporations, many of whom are waiting for the first large update patch.

Personally I wasn't too excited with Vista at launch, it didn't feel like a significant improvement from windows XP and at times even a downgrade.
So for the sceptical, Microsoft will also release SP3 for windows XP.