The return of the centrally supported wing
Watching the recent car launches for the 2006 F1 season, I note that the new Renault (R26) and Ferrari (248) cars have central pillars supporting the mainplane of the rear wing. It was done first (in recent times) by BAR on their BAR007 last year and the reason is that it reduces the weight of the entire wing assembly at the cost of a small amount of extra drag.F1 used to have the wings centrally supported with the endfence suspended from the main plane of the wing. This is the arrangement used currently by IRL cars. When teams started to maximise the length of endfence they needed to support the lower end of it laterally. If you have a full-height endfence you can use it to support the upper wing - there is no longer any need for the central support. As diffusers were not commonly in use at this time, early examples used a beam (basically a length of aluminium tube) to connect the end fences to the gearbox.
When diffusers came into use it became advantageous to shape this support beam like a wing and use it to increase the effect of the diffuser. Thus the lower wing element is often called the beam wing.
The problem with this arrangement is that all the drag on the main wing and the end fences applies a torque to the beam wing. In addition, the downforce takes a very circuitous route as most of it is developed in the centre of the main wing and causes a bending force on that, then compression on the end fence and then a bending force on the beam wing before being applied to the gearbox (or the crash structure these days).
By putting the central support back in, all the main loads travel directly through that support to the gearbox/crash structure. As a result the main plane of the upper wing and the beam wing can be made much lighter. You have to add the weight of the new central support obviously, but because the loads on that are in compression, it doesn't have to be very strong/heavy.