This Microsoft article indicates that Windows Vista SP2 may indeed be on its way, and one could expect it in early May 2009. It talks of some WU Vista SP2 Prerequisites.
Tuesday, April 28, 2009
New security content: To be announced
New non-security content:
Update for Windows Server 2008 and Windows Vista (KB955430)
Deployment: Important/Automatic Updates, WSUS, and Catalog
Classification: High Priority, Non-Security
Target platforms: Windows Server 2008 and Windows Vista
Approximate file sizes:
Windows Server 2008 for IA-64 update: ~ 14268KB
Windows Server 2008/Windows Vista update: ~ 4287KB
Windows Server 2008 x64/Windows Vista x64 update: ~ 10148KB
Install this update to enable future updates to install successfully on all editions of Windows Server 2008. This update may be required before selected future updates can be installed. After you install this item, it cannot be removed. This update is provided to you and licensed under the Windows Vista and Windows Server 2008 License Terms.
Click KB894199. An indication of things to come?