Exchange 2007 Global Address List in Cached Mode

Basically the GAL works like this:

-Information is entered into an account in Active Directory.
-The Exchange GAL is then updated to reflect that change on the server at a set time, typically every 24 hours as seen in the Exchange Management Console under Organizational Configuration-Mailbox-Offline Address Book tab.
-A differential file is created on the Exchange server with the updates and the Outlook client must then connect to the Exchange Server at set intervals (typically every 720 minutes/12 hours) to pull the updates.

Note: The Hierarchy Table Recalculation is set on the DC at 720 minutes but is not recommended to be changed. NTDS\Parameters\Hierarchy Table Recalculation interval (minutes)

In cached mode, you won't immediately see the updates made to the GAL. You can however, force the update by going to Tools-Send/Receive-Download address book but this will only show changes once the Exchange Server has updated its Offline Address Book file for the client (Outlook) to download.

One could force the update on the Exchange server by using the Exchange Powershell (you cannot update the GAL from the Management Console)

Update-GlobalAddressList -Identity -DomainController

Note: Running this command only starts the process, it can take several hours to complete.

So essentially if you make changes to a user account in Active Directory, you can't really expect things to update across the network immediately. This is by design so that the network isn't clogged by numerous and frequent GAL downloads.

For more info see:

Administering the OAB in Outlook 2003 and 2007
Exchange General FAQ
Update the Global Address List