Update *April Fools*
In a move that's been rumored of since the development of Viewer 2, Linden Lab has announced it will no longer continue to keep Second Life's Main Grid accessible to Viewer-1 based viewers, "It's been over two years since the last version of this viewer was released. Continuing to support it has been holding back the Grid," CEO Rod Humble stated in the official blog, "and continuing developments in technology are threatening to render Second Life behind the times. Residents whom do not adopt more recent Viewers will find themselves having more and more difficulty getting about the Main Grid, eventually unable to access it at all."
However, Linden Lab is giving those still insisting on using the old Viewer 1 and third-party viewers based on it's technology a continued means to access Second Life. It plans to set up another grid separate from the main one. Residents can freely move between the two, provided they are using the correct viewer. Some items in their inventory will only be able to work properly in one grid, such as Mesh objects. Residents can move their private sims and mainland holdings to the Viewer 1 grid as well, for a fee.
Linden Labs has designated the new Viewer 1 Grid the Low Use Resident Grid, or "LUsR" Grid. It is also referring to residents who will be exclusively using this grid as LUsRs, "Should a resident desire to drop their LUsR status, all they have to do is start using the proper viewers and they will be able to travel about normally and not be confined to the LUsR grid as LUsRs."
To read the official post on the Linden blog, Click Here.