Microsoft has announced at TechEd that the public beta for Service Pack 1 for Windows 7 and Windows Server 2008 R2 will be released sometime in July. Do note, though, that for Windows 7, Service Pack 1 will not include any additional functionality, only updates that are currently available. So, technically, you could roll your own SP1 for Windows 7 if you were so inclined.
While the new features for Windows Server 2008 R2 benefit Windows 7 by providing a richer VDI experience, SP1 will not contain any new features that are specific to Windows 7 itself. For Windows 7, SP1 will simply be the combination of updates already available through Windows Update and additional hotfixes based on feedback by our customers and partners. In other words, customers can feel confident about deploying Windows 7 now!