Paul Thurrott posted a preview on Windows Vista Service Pack 1 Beta

As you can see from the accompanying screen shots, there just isn't all that much to see yet: Windows Vista Service Pack 1 (SP1) functions like a traditional Windows service pack, aggregating previously released fixes and adding just a few features, none of which appear to expose themselves in the UI. Will there be more palpable changes later in the SP1 beta? Possibly. But Microsoft has been very careful to lower expectations, noting specifically that SP1 will not include a new Media Center version, for example.

Windows Vista Service Pack 1 Beta (v.249) Notes and Screenshot Gallery