The social desktop would need more dimensions in order to include the social interactions as a basic construct of the platform. The social desktop should also be contextual being able to bind to a physical context (where) and enable the creation and detection of social context (who) based on situation and history.
I can think of the following dimensions that would be needed
Content - This mirrors the traditional desktop notion of content (which is typically stored in files) but includes a more decentralized notion of storage model where local storage is merely a cache of a far larger online storage of content spread across a number of distinct services (chosen by the user). The desktop itself is merely and integration point for this content.
Community - This is a new dimension and goes to the core of the social desktop which is about maintaining links with my colleagues, friends and family (my tribes). Again the virtual representation these communities will be encapsulated in separate services which can be integrated at the desktop. Different user roles will naturally align with different communities. This dimension also deals with community data in its various form. This includes the sharing for information from the content dimension into a community but also the ranking/rating, bespoke authoring, communication, commentary and narration of community information.
Time - The time dimension deals with present, past and future events for the user. It also is the natural home for presence and status information which may in turn be reflected into the community dimension. Time is an important part of the social desktop not only as an organizational tool for dealing with schedule and role based activities but also to navigate and search across a time line.
Context - The social desktop assumes mobility and mobility leads to location which in turn bring in specific services and information (LBS) as well as enable the discovery and use of shared resources that are local. Context can binding specific system functions to local and learned services (e.g printing).
More thinking is required for the rendering model, the simply direction is to just replicate the existing desktop canvas but a more optimum layout and organization model might be better.....more later.