Check out Migrating Exchange from HMC 4.5 to Exchange Server 2010 SP2. It contains a white paper and PowerShell scripts. Together they provide the recommended and supported migration path from HMC 4.5 to Exchange 2010 SP2. The steps in the guide may also be helpful when migrating from non-HMC environments that have configured some form of multi-tenancy.
Coming soon will be a guide to help you migrate from Exchange /hosting mode to Exchange 2010 SP2 installed without the /hosting switch.
I hope this helps you with your plans to migrate to Exchange Server 2010 SP2.