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
One thing that should stand out with these two CMDlets is that policies could only be associated with mailbox accounts. Why would you ever want throttling policies associated with anything else? I'm glad you asked. There're at least two valid scenarios to consider.