Do you need Vista SP1? Yes and No

It's always good to install the latest code for any OS, but this update could mean a few hours  of work without tangible improvements. Cnet Reviews

The good: Windows Vista SP1 improves the overall upgrade process, fixes hundreds of tiny problems, and makes it easier for third-party vendors to write stable code for Vista.

The bad: Windows Vista SP1 lacks any compelling "must haves," and, in most cases, doesn't significantly improve performance (in some cases, it even degrades performance).

The bottom line: While it's always good to install the latest code for any operating system, installing the Windows Vista SP1 update will require some casual users to spend a few hours without any visible or tangible improvements to their systems.