Earlier today the Exchange CXP team released Update Rollup 5 for Exchange Server 2010 SP1 to the Download Center.
This update contains a number of customer-reported and internally found issues since the release of SP1. See 'KB 2582113: Description of Update Rollup 5 for Exchange Server 2010 Service Pack 1' for more details.
Read more over at the MS Exchange Team blog.
Technology Architect/Writer/MS Vendor
MCM: Exchange Server | MVP: Exchange Architecture