An update to Orcas SP1 is being rolled out that will be available through Windows Update. The update contains application compatibility fixes for the .NET Framework following the Orcas SP1 release. If for some reason you need to install it directly, the downloadable package is available now.
There's one fix in the update that affects WCF serialization. We fixed a race condition that caused an exception in System.ServiceModel.TypedHeaderManager due to the same type being added to the cache twice in rare cases.