For many 3D users of AutoCAD, the ViewCube is likely to be the most useful new thing in AutoCAD 2009. There are a couple of problems with it, at least in the Release Candidate:

1. It does not work in 2D wireframe mode (which is, paradoxically, where 90% of my 3D work is done). You need to choose another visual style before it will appear.
2. It seems to slow things down quite a lot in complex drawings.

That said, if you have more than enough computing power for the drawings you usually deal with, then this is a very, very nice interface addition. You can just pick intuitively on the various parts of the ViewCube and your view of the model changes accordingly. You can also click and drag on the cube, and it will move where you place it, while snapping on to the various 45 and 90 degree view directions when you get near them, in the same way that Polar snap works. There is a right-click menu with a bunch of useful options, including a quick and easy switch between parallel and perspective views.

You can also easily switch between User Coordinate Systems using the little menu thing under the cube. Unlike some of AutoCAD 2009’s new user interface elements, the ViewCube looks like a finished, polished tool and provides a genuine boost to productivity. Beautiful.