*** Update ***
See the offical blog post for guidance. Luckily Exchange 2007 SP3, Exchange 2010 RTM and Exchange 2010 SP1 are supported after all.
I see more and more questions from folks asking whether it’s supported to install Exchange 2010 SP1 on Windows Server 2008 R2 with the new SP1 applied or even upgrade an existing server Exchange 2010 SP1 server running on Windows Server 2008 R2 to this new service pack. There’s still no information about this in the Exchange Server 2010 Supportability Matrix , but according to the Exchange team this is not supported with the current Exchange 2010 SP1 build but will be with Exchange 2010 SP2 (or with some luck with a future Exchange 2010 SP1 roll-up update). The Exchange team will post something on the Exchange Team blog about this very soon, but I thought I get the message out until that happens.
Thanks to David Espinoza and Nino Bilic!
Technology Architect/Writer/MS Vendor
MCM: Exchange 2007 | MVP: Exchange Architecture