This is really neat. The Exchange Deployment Assistant has been updated to include the migration and configuration requirements to allow rich co-existence between your on-premises Exchange infrastructure and Office 365 – Exchange Online.
Deployment Assistant has been enhanced to include rich coexistence information for those interested in maintaining some users on-premises and some users hosted by Microsoft Office 365 for enterprises in the cloud. This approach is different than the Simple Exchange Migration (SEM) and Staged Migration options currently offered by Office 365. As of now, the available scenario is targeted solely at those organizations with a current Exchange 2003 on-premises implementation, but additional scenarios for supporting Exchange 2007 and Exchange 2010 will be coming. The coexistence information is also only available in English at this time.
Take a look here: Exchange Server 2010 Deployment Assistant.
You have to remind yourself that the service is in beta and this guide is a work in progress. There are a few errors and in a few cases tasks are out of order when compared to the old guide. Since this new guide is presented in Silver Light, you cannot copy information directly from it, however, if you click the pint icon, and then cancel printing, the content appears in a new window that you can copy content from.