Microsoft is working on next version of Active Directory Migration Tool (ADMT) tool. You can participate in the ADMT 3.2 Beta program though http://connect.microsoft.com site.
About ADMT 3.2
The Active Directory Migration Tool version 3.2 (ADMT v3.1) simplifies the process of migrating objects and restructuring tasks in an Active Directory® Domain Service (AD DS) environment. You can use ADMT 3.2 to migrate users, groups, computers, and Managed Service Accounts (new in ADMT 3.2) between AD DS domains in different forests (inter-forest migration) or between AD DS domains in the same forest (intra-forest migration). ADMT can also perform security translation (to migrate local user profiles) when performing inter-forest migrations.