I think every exchange admin has come across this issue in which users complain that they can’t find the new staff in the Outlook address book. There are a number of solutions like instructing the user to use OWA or Outlook online mode if it is really urgent, downloading the address book (after the server has updated it) etc.
But, a simple solution that I have come across for the issue is to instruct users to select “All Users” from the address book. This will force Outlook to get real time data from the server and the user will be able to find the new staff.
--> The rest is on the blog : http://www.howexchangeworks.com/2011/09/finding-new-user-in-gal-while-in.html