We are looking to move to the NextGen UI , lookin for any advice on do and don't do?
If you have training materials for your company, I would highly recommend changing yourself to NextGen and updating all the training documents before you switch on the new UI for others. We also switched on one country at a time, so if you group employees, that may be a good way to roll it out. We had so many Concur users, we didn't want our helpdesk overloaded with calls, so rolling it out slowly worked best.