I have recently upgraded from Exchange 2003 to 2010 and followed all applicable guidelines on how to do this successfully, and have successfully decommissioned our old 2003 box.
Some of my Outlook (2010) clients have reported that their Global Address Book is not up to date, I have checked this and found that it reflects the old GAL and is not showing any updates or changes. I have confirmed that the GAL is fine by accessing via OWA with no issues.
I am aware that the usual fix for this is to rename the 'Offline Address Book' in the client's profile, which I did by script for everyone, which worked! But the next morning after the Address Book update, quite a few (not all, but no relation between from what I can see) reverted back to the previous OAB.
I am not sure what other details to post here other than it's Exchange 2010 on a virtual box (regardless) with all clients running Outlook 2010. I have followed as much as I can which relates to the Exchange EMC as I do not want to blx things up using Shell, but all detailed advice appreciated where the Shell is concerned.