The jump from SMF 1.1 to 2.0 is actually a major upgrade. The majority of changes won't be noticeable because they're internal. However, things like the drop-down windows in the main menu and how different areas of the forum look/are organized, particularly places like members' profiles, will definitely be noticeable. But I'm sure we'll all get used to everything before too long.
The forum's Help section will definitely be our friend.