As far as UI changes, the two biggest differences that you'll notice right away are the dedicated screenshot button next to the multitasking button, and the ubiquitous dock tray at the bottom of the screen which adds 6 app links on all homescreens (nothing Apple-esque about that edition, eh?) Samsung has also prettied up some of the stock Android apps, and added a social networking widget and a nicer quick settings panel. There is also reportedly a photo editing app, but it hasn't gotten much praise, and The Daily news app is loaded in.
Behind the scenes, the update adds support for DivX video, Bluetooth 3.0 and Samsung's AllShare DLNA. Definitely a lot of good stuff in this update, and it should be rolling out soon. And, for those of you who may wonder, it has been confirmed that you can root your Tab again with the same tool as before even after applying the TouchWiz update.