Wow they’re really different thanks to all of the new social media capabilities. The UI is wayyyyyy better, somewhat easier to brand, and they integrate and expose social functionality like status, feeds, colleagues, social search… each user has a “wall” (to use Facebook terminology)… They’re the hub of much of the new social functionality (search centers expose much of the rest)
Behind My Sites (and the User Profile service application and ALL service applications) is the new service application model, which among other things allows you to manage performance and redundancy of each service much better than you could in 2007, AND to share services across farms. So imagine if you have two farms: NYC and Tokyo. You could actually host mysites on one farm if that made sense from a topology perspective and share that service across both farms. Or vice versa–you might have a shared Metadata service (likely) and dedicated user profile service applications (and therefore mysites). Bottom line: your topology choices are much better!
And User Profiles now do Sync rather than import only. So if you want to write back profile properties from SharePoint to Active Directory you can do so
One of the “little things that mean a lot” with MySites: the new organizational browser is a silverlight control that displays your organizational relationships (org chart) BEAUTIFULLY. In fact it’s so pretty someone thought I was browsing a site designed by a fruit company!
To Spencer’s point about writing BACK user profiles; that’s HUGE. A lot of companies want a directory that users can maintain–now you can do that as much or as little as you want.
FWIW behind the scenes of User Profile Sync is a built-in version of Forefront Identity Manager. While you don’t NEED to go “behind the scenes” with FIM, if you do it is quite interesting how it works, and how it manages the various user profile sync tasks.
IMPORANT: If you’re going to set up user profile sync, READ THE DOCUMENTATION! Among the most important notes is that, to configure user profile sync, the farm service account (the account used by central admin and the timer service) must be a LOCAL ADMINISTRATOR on the SharePoint servers. That’s just for configuration of UPS, then you can pull it out of Admins (and you’ll get Health Analyzer reminders to that effect). If you don’t put the farm account in Admins, you’ll have lots of headaches! So with that, keep in mind that if you use the Farm Configuration Wizard to set up multiple service apps, either de-select (don’t configure) UPS or make sure that the farm account is a local admin at that time.
<i>This question was answered by Spencer Harbar, Enterprise Architect at Microsoft and Dan Holme, Consultant and Trainer, Intellium.</i>