Exchange 2010 SP1 RU1 is released, you can download it from here http://www.microsoft.com/downloads/en/details.aspx?FamilyID=a371fa96-e85b-4a4f-8242-15d56595d0ec&displaylang=en

Note for Forefront users

For those of you running Forefront, be sure you perform these important steps from the command line in the Forefront directory before and after this rollup's installation process. Without these steps, Exchange services for Information Store and Transport will not start back up. You will need to disable ForeFront via fscutility /disable before installing the patch and then re-enable after the patch by running fscutility /enable to start it up again post installation.