One of the biggest changes to Revit 2011 has been in the UI and how you get around. The changes, honestly, are very subtle but very profound because of how you use work with the interface is so impacted.
The two big changes for me are the Modify panel on the Ribbon and the Properties Palette.
For the ribbon, now whenever you work with objects, the tools that are consistent between all objects are to the left side. There is a division (see fig) and then to the right are the tools that are applicable to that object. It solves a complaint in 2010 in that tools moved around and made it hard to find to what you wanted. Now there is a level of consistency that should help. As anything, as you use it, you get used to it.
The other big thing for me is the new Properties Palette. Basically an on-call dialog with either view or object property parameters. I kinda like having it at the ready, but I will admit I have to widen it up to see more data. Then I thin it back. I suppose as I move into using it for production work it will end up sitting on a second monitor and be wider all the time. At the top of this puppy is the Type Selector. Seems like a good place for it to go, with a big image of the active family. If that placement isn't as helpful as one would like you can add it to the Quick Access Toolbar. From there it is much like it as in the past on the Options Bar.