Problem:
If you think moving mailboxes to Exchange 2010 SP1 is slow and taking longer time than in RTM version, here’s why!
In RTM Exchange it was doing 5 parallel moves at a time, but in SP1 Microsoft changed MaxActiveMovesPerTargetMDB from 5 to 2 concurrent moves.

What is changed:
RTM values:

MaxActiveMovesPerSourceMDB: This property indicates the number of mailboxes that can be moved on the source mailbox database at one time. The default value is 5 concurrent moves.
MaxActiveMovesPerTargetMDB: This property indicates the number of mailbox moves that can be moved on the target mailbox database at one time. The default value is 5 concurrent moves.

SP1 values:

MaxActiveMovesPerSourceMDB: This property indicates the number of mailboxes that can be moved on the source mailbox database at one time. The default value is 5 concurrent moves.
MaxActiveMovesPerTargetMDB: This property indicates the number of mailbox moves that can be moved on the target mailbox database at one time. The default value is 2 concurrent moves.

The change in MaxActiveMovesPerTargetMDB in SP1 means that we can only do 2 concurrent connections.

The workaround:
Pull open Notepad. If you have UAC enabled, be sure to Run as Administrator. Browse to the install location of Exchange and open the following file:
C:\Program Files\Microsoft\Exchange Server\V14\Bin\MSExchangeMailboxReplication.exe.config
you can change
MaxActiveMovesPerTargetMDB back to 5 to allow 5 concurrent moves.
Save the file, and restart the Microsoft Exchange Mailbox Replication service and do this configuration change on all your CAS servers.
Review the other settings to make sure they reflect what you’d like to see in your environment, and to ensure you’re not getting throttled on any other setting that may pertain to what you’re trying to accomplish.

These lines control the upper and lower limits for these settings:

MaxActiveMovesPerSourceMDB - 5, 0, 100
MaxActiveMovesPerTargetMDB - 5, 0, 100

Links:
Increasing the number of simultaneous Remote/Local Move Request on Exchange 2010 (http://madoxr.blogspot.com/2010/01/increasing-number-of-simultaneous.html)
Understanding Move Requests (http://technet.microsoft.com/en-us/library/dd298174.aspx)