Use Outlook in Cache and Online Global Address List

You can use Outlook in cache mode and still have the client access the Global Address Book online:
If you make frequent changes to the offline address book, you may want to modify the way that Outlook computers on your network access the Address Book. You can disable the downloading of the offline address book and force the Outlook computers to use the online Global Address List when they use Cached Exchange Mode.
To do this, add the following registry value to the computers, as appropriate for the version of Outlook that you are running.

Outlook 2010
HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\Cached Mode
Parameter: DownloadOAB
Type: REG_DWORD
Value: 0
Outlook 2007
HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Cached Mode
Parameter: DownloadOAB
Type: REG_DWORD
Value: 0
 
We highly recommend Cache mode for outlook users for the reasons stated in the blog site below:
 
http://blogs.technet.com/b/neiljohn/archive/2011/06/15/outlook-2010-network-latency-test-results.aspx