This post discusses about User Profile Service Application changes in SharePoint 2013. One of the key change is better performance in Active Directory Profile Synchronization. It reduced the import time from up to 2 weeks down to 60 hours for extremely large organisations having 200K users. This has been tricky in earlier versions. Several optimizations are already been added in SharePoint 2010 like Adding indexes to certain user properties and importing data from BDC in batches.