This only effects people that use a directory service (LDAP) for addressing emails, but it's a big deal for those of us that do. SP2 for Office XP (including Outlook 2002) contains the fix for a problem of searching for users matching entries in the To, CC, BCC lines. In prior versions, you were likely to get an error like this:

<font color=red>Unable to display results because too many entries in the Internet Directory match your search criteria.</font color=red>

The SP2 improves the search behavior, and there's a new registry entry to further limit the search and increase the success rate.

See;EN-US;Q311829 for more information.