You may find that Login Scripts are very slow to run when you are using any of the following operating systems:

Windows Vista – SP2, Windows Server 2008 – SP2, SBS 2008 – SP2, Windows 7 – SP1, Windows Server 2008 R2 – SP1 or SBS 2011 – SP1

The boxing feature causes the login script to run at a reduced priority for the first 60 seconds, a hotfix is available from Microsoft that improves the speed at which the Login Script runs.  This can be found in the Microsoft knowledgebase under KB 2581608 http://support.microsoft.com/kb/2581608