Microsoft made some changes (“boxing”) to startup programs that will help prevent programs like Adobe Updater, WinZip quicklaunch, and other startup programs from taking all the resources of a system.  Vista sp1 sets a low-priority thread and low-priority disk access that will affect ADSI queries or disk access used in logon scripts.  Read more about it here: http://bink.nu/news/boxing-and-the-case-of-the-slow-or-hanging-logon-script-in-vista.aspx