If you previously implemented Exchange Server 2010 RTM and after a while ,you upgraded to SP1, you should realize about mailbox move process times.Now it is taking more.
This is because parallel move values is set to 2 on Exchange Server SP1.
In RTM version;
MaxActiveMovesPerSourceMDB : Number of mailboxes that can be moved on source mailbox database.Default value was 5.
MaxActiveMovesPerTargetMDB : Number of mailboxes that can be moved on target mailbox database.Default value was 5.
But in Service Pack 1;
MaxActiveMovesPerSourceMDB : Default value is 5
MaxActiveMovesPerTargetMDB : Deafult value is 2
That means we can only move 2 mailbox concurrently.
Also you can edit your MSExchangeMailboxReplication.exe.config file and customize as you want.