13. A system of rendering a virtual environment, said virtual environment having a virtual model, comprising: an input interface for identifying a user entering the virtual environment and user context in the virtual model; a rendering engine for rendering an output of the virtual model using objects in the virtual model; a difference engine for locating, in associated user memory, previous versions of the objects in the virtual model and for identifying specified differences between the objects in the virtual model and the previous versions of the objects located in the user memory; and wherein said rendering engine is further adapted for rendering a layer of the identified differences on the rendered output of the virtual model by modifying the objects in the virtual model based on user preference, and wherein an identified difference is rendered differently than another identified difference according to the user preference and according to type of object.
18. A system according to claim 13 wherein an object that exists in the user memory but is no longer in the virtual model is shown as a diminished image in the virtual model.