ExchangeTeam blogged about two new cmdlets related to throttling.
Exchange 2010 SP1 introduces two new throttling cmdlets: get-ThrottlingPolicyAssociation and set-ThrottlingPolicyAssociation. In Exchange 2010 RTM, in order to determine which throttling policy was associated with a given user, you would use something like:
Get-Mailbox JohnDoe | fl ThrottlingPolicy
To assign a non-default throttling policy to a user you would call
set-Mailbox JohnDoe -ThrottlingPolicy Foo
Read more at source: http://msexchangeteam.com/archive/2010/08/02/455707.aspx