Active Directory Migration Service (ADMS) is a could based Active Directory migration service (not a solution) from Microsoft. Behind the scene they are using ADMT and FIM. Directory synchronization was a big drawback of ADMT. The combination of ADMT and FIM can overcome all these challenges.
Also, the self migration portal provides an end user driver migration option.
You can see a demo on the Channel9 site - http://channel9.msdn.com/Blogs/Taste-of-Premier/Taste-of-Premier-Directory-Consolidation-with-Windows-Azure-Active-Directory-Migration-Services