Very labour intensive, especially if there are lots of little detail bits on your car (like that Porsche's spoiler). I once enquired about wrapping for my van, as I had thought about having it lettered (and all those Sky vans running around have it done) but the price put me off, just as well as the business doen't pull in a lot of money!
I can see the advantages for a matt black finish, since I believe if you order (for example) a matt black BMW 3 series, the care you have to give it is quite offputting. A wrap, on the other hand, I'd presume could just be washed like a normal paint finish (as long as you don't use a steam cleaner).
Quoted from another site:
"BMW is apparently requiring all owners to sign a "maintenance agreement" that insists the M3 is never polished or waxed, ran through an automatic car wash or even strongly rubbed. Additionally, BMW politely asks that you immediately remove bugs, bird droppings, tree sap and fuel spills with a soft sponge, and naturally, dealers are more than willing to sell you appropriate products for maintaining the matte finish.
According to enthusiast site Bimmerfest, BMW explicitly states the M3's warranty won't cover any damage due to owner neglect and it notes that all exterior repairs must be performed by a BMW-authorized shop. What's more, if you don't sign the agreement, no Frozen Grey M3 for you..."