This article explains which upgrade paths are supported from Exchange 2003 to Exchange Server 2010, and under what scenarios you would want to use Exchange 2007 as an interim upgrade path.
When Exchange Server 2010 was released some customers assumed that the similarities between Exchange Server 2007 and Exchange Server 2010 would allow in-place upgrades to occur. Microsoft has released a video to explain why this is not the case.
Microsoft has released Exchange Server 2010 Service Pack 1. Organizations already running Exchange Server 2010 (RTM) can upgrade to Service Pack 1, however the upgrade must be planned out properly to ensure a successful outcome.
