My wife's absolutely favorite feature of Outlook is the fact that she can use the auto complete feature to address her emails. I will never forget when I had to setup her computer fresh and reinstall all the software. Back then I did not know about the NK2 file. All I knew is she asked where her email address shortcuts went and I of course did not have a clue. So after some research I learned about the NK2 file. By moving and backing up this file I could always give my wife her favorite feature if I ever had to reinstall Outlook or get her updated on the laptop for travel, etc. with the most recent version of her auto complete list.
In Outlook 2003 and 2007 the NK2 file used for auto complete is located at Drive: \ Documents and Settings \ Your User Name \ Application Data \ Microsoft \ Outlook \. This is a hidden directory so you will need to choose to view those hidden folders in order to drill down to that directory and find the file. The change that has occurred in Outlook 2010 is not the removal of the auto complete feature - just where that list is stored and how it is presented in Outlook itself.