The Microsoft Exchange Server Deployment Assistant now support Cloud and On-premise + Cloud deployments in addition to On-premise only. This is pretty exciting and will be a great boost to help those looking to upgrade to cloud or hybrid Exchange solutions.
You will need to have Exchange 2010 CAS role on-premise to migrate or to setup a cross-premise deployment. For now only Exchange 2003 is live, with 2007 and 2010 to come soon.
Exchange Server Deployment Assistant: http://technet.microsoft.com/en-us/exdeploy2010/default.aspx#Index
The tool walks through setting up DirSync and ADFS 2.0 to support identity federation. So if you are considering Office 365, another hosted solution or just a plain old on-premise upgrade head over to the tool.
On a related note, I am pleasantly surprised by the number of organisation I come across now using Microsoft Online Services ranging from small to very large.