Windows Server 2008 R2 and Windows 7 Service Pack 1 provides further improvements and hardens these Operating Systems. Although, SP1 includes previous updates which many organizations and users have deployed through Windows Update, Windows Server Update Services (WSUS) or third-party patch management systems, it is quite often the practice to use a Service Pack as a baseline. That is, having successfully deployed a service pack throughout the organization creates a reference point or standard which puts your mind at rest. Some machines or even servers might have missed some updates or an administrator might have skipped some problematic updates intentionally. By time, patch management standards are likely to end up in a mess!
However, before going for a full deployment of SP1 I suggest that you test your environment. If patch management inventory is available, look for machines that lack updates with respect to others and find out why. Test the most critical machines in a test or staging environment before updating production ones. Where possible, follow Microsoft recommendations before applying SP1 and run the System Update Readiness Tool to resolve update inconsistencies. There have been issues with some devise drives, hence it is recommended to update these with the latest versions and some users are reporting SP1 installation failures with an unknown error.
As most organizations run their servers in virtualized environments, you might encounter similar problems while SP1 tries to access some virtual devices. In fact, I had to disable guest add-ons on my virtualized setup in order to be able install SP1 successfully. For more details about this error and the troubleshooting steps I performed to find the problem go here.