Leonid Nemirovsky of the Better Than Nothing AutoLISP site shares a few tips on using 2D operations in a 3D environment while working in AutoCAD.

"While in 3D, it is possible to use certain 2D commands (to some degree) like Rotate, Move, Mirror, etc. Just set your view to Top, Left, Right, Bottom and be sure that Ortho is on. Be very careful with osnaps — better yet, turn them off."

Notes from Cadalyst Tip Patrol: Technically, all 2D commands work in 3D in AutoCAD. In fact, if you are working in AutoCAD, you are working in three dimensions, even if you are not. AutoCAD works on a Cartesian Coordinate System using three axes (AutoCAD calls it the World Coordinate System).

When a 2D drawing is created, the Z axis is set to an elevation of zero. Therefore, you are working in a 3D environment but only taking advantage of two dimensions. By default we work in the Top view. Think of the views as being the sides of a cube: Top, Bottom, Left, Right, Front, and Back. You could move to any of those views and work in two dimensions. If you share files, however, you will probably run into issues, so I suggest you don’t do this.

Leonid’s point is that you can use "regular" 2D commands even if you are working with a 3D model. It is very easy to do so if you switch your view to one of the six default views. Once you’ve done this, you can ignore the third dimension and manipulate your objects on a 2D plane with ease.