WhiteBlue wrote:But what is it going to give the owner that a aluminum monocoque can't give?
Nothing. Why the entire industry is moving to carbon fiber is beyond me.
Here's the relevant bit of the previous article which you didn't read. In the future, it would be most helpful if you would take the time to read through a thread before commenting.
McLaren Automotive uses composites only where they bring major benefits and prove to be cost-effective. Santoni still uses metal in many areas where other automotive companies have started to use CFRP. For example, the rear structure, which carries the rear suspension, engine and gearbox, is a spaceframe made from welded aluminum extrusions. Cost and early uncertainty about engine operating temperatures drove this decision. Similarly, the front energy-absorbing tubes are aluminum extrusions that can be replaced inexpensively after a minor impact. And unlike the Aston Martin DBS (see "Gurit CBS for the Aston Martin DBS," under “Editor's Picks”), which makes use of Gurit’s (Newport, Isle of Wight, U.K.) CBS composite panels, most of McLaren’s body panels are aluminum or sheet molding compound (SMC). In particular, the rear quarters and the doors, which have a complex double curvature, are manufactured by Sotira (Change, France) from glass fiber-reinforced SMC.
When it came to the passenger cell, however, CFRP was clearly needed to take the high loads from the varied design requirements. In keeping with the principle of a strong composite driver’s cell developed in McLaren’s racing cars, the new road car has a monolithic CFRP cell structure known officially as a MonoCell, but nicknamed the “tub.”
The tub forms the main structure of the car. It takes most of the road loads via a subframe at the front, but it also handles the seat belt loads and, ultimately, the crash loads. The main mechanisms for passenger protection are the previously noted aluminum front and rear crush structures, which crumple to absorb impact energy, leaving the tub undamaged to protect the occupants, even during severe impacts. The success of this design feature has been demonstrated in the crash test program. A single tub has been used in no less than three high-speed impacts, without sustaining significant damage.
The one-piece structure incorporates several hollow sections. Some smaller voids are filled with Rohacell foam from EVONIK Röhm GmbH (Darmstadt, Germany), but the biggest sections are left hollow with removable mandrels. The total volume of these cavities is a massive 120 liters/33 gal (US), keeping tub weight to a mere 176 lb/80 kg.
Although the tub’s immediately apparent function is to carry the main operating loads between the front and rear of the car and protect the passengers, Santoni developed other criteria for its design, including the less obvious requirements of corrosion prevention, overall structural stiffness and ease of access to the passenger compartment.
Corrosion has been a problem in some expensive cars that are made in small numbers, especially when there is a reasonable customer expectation that the expensive new car will survive long enough to become a classic car. McLaren’s use of a composite tub avoids corrosion in the floor and hollow structural sections where metals are most likely to fail.
The hollow sills along the tub sides enhance the stiffness of the tub and, therefore, the car’s overall structure. The sills’ unusual width overcomes one problem common to most supercars, that of getting in and out of a low passenger compartment over a high sill. In the MP4-12C, exiting passengers can sit on the sills as they slide out of the seats.
Although the tub is well protected by crush structures, most areas of the tub are repairable, if necessary. But the design philosophy is that in most moderate frontal accidents, the damage will be limited to the extruded aluminum energy absorbers, the body panels and, possibly, the subframe.
In any case, tub maintenance is expected to be minimal. “The service intervals of modern carbon fiber aircraft have doubled those achieved by aluminium designs,” Santoni points out, noting that this is “a testament to the superior longevity of a carbon-based structure compared to aluminium.”
In line with the company’s policy that carbon fibers are in the vehicle to do a job, not perform cosmetic or marketing functions, McLaren designers resisted the temptation to have CFRP in the MonoCell visible to the customer. The interior of the tub is covered almost entirely with good-quality carpet.
and got stolen first time i left it in the garage instead of taking it into the house... 
