indeed, networking is very important. I have built up some good connections at the Ferrari dealership in belgie these past few years and I've been able to shoot some of their cars.
although i'm not allowed to do any spectacular stuff, I am more than happy with the stuff that i am allowed to do. The rules are as followed:
* Dealership owned cars, showroom:
- have 0 miles on them, so can not be moved/started/go outside
- take off my shoes when I deem it necessairy
- no tripod's on the seats for interiour shots, on the floor it's ok
- I get to have the key so that: I can open the windows, put on the dashboard lights or open the convertible top. NO STARTING!!!
- no flash photography inside the showroom when customers are there (empty dealership = flash as much as I want)
* Dealership owned cars: demo models and testdrive models for customers
- cars can be pushed on the terrain of the dealership, not on public roads, as much as I want when I use the special gloves they provide (no scratches or fingerprints on the perfectly detailed cars).
- cars can be started when necessairy, no revving the engine when it's cold.
- cars can be moved by a mechanic (driving) as long as I don't ask to move it 5 times per hour 
- certain cars can be driven to a location I use for them, but only when they request that I take pics of that car. It's about 2 miles down the road next too a lake
- the car's can be driven by me with dealer plates, but under strict regulations. I am not allowed to break the speedlimit (obviously), I have to be precise about the route that I will take, when I am going to be driving the car and how long I will be gone. They do check the milage I do so no cheating. Gas is payed for by them. The maximum distance I can cover is anything in a 20 kilometer radius (about 12.4 miles) around the dealership.
- I have too keep them as clean as possible
- Tripods are allowed inside, as long as a put something under the tripod's feet to protect the car's interiour
- some other non important stuff
* Privately owned cars, showroom:
- The privatly owned cars are usually there for 2 reasons: finding a new owner OR stocking them for the wintertime
- no starting inside the building
- when the owner of the car asks me to take pictures, we can take the cars outside (can't do that with the dealer owned cars)
- when the car is outside I can do pretty much anything I want too with it, as long as the owner agrees. Hell, if some nutcase allows me too, I could even take one too the south of france for a photoshoot in monaco or something 
- the dealership is not responsible in any way for traffic fines/petrol used/damage in any way. I have too make an agreement with the owner himself.
- when the cars are in the showroom to stay there during the winter, I have too keep away from them. They are not going to call the owner to ask him and stuff like that, that would be rude. Exteriour is ofcourse allowed, since the cars remain in the showroom without there licenseplates.
that's about it for my rules. they did make an exception on the Ferrari Enzo after I kindly asked, they pushed it outside for me but under no circumstances was starting it an option, to push it outside they didn't even get it off the handbrake. They used special carts that go under the wheels to be able to push the car away. they even brought it to the photolocation down the road on a flatbed truck, but that was only after a few months when they decided they needed good pictures to actually sell the car.
I've been going to that dealership for about 3 years now and up until today I have only once gone out with a privately owned car, it was a 355 F1. I did about 100km in that car and had one hell of a good day. the owner let me drive it between locations but was always with the car, the entire day. I did that shoot for free 
In the dealer owned cars i've gone out in a 430 spider and in a 360 coupé. but only too the photoshoot location so about 4 miles in each car and never above 40 mph. all the other times the cars we're driven to the location by a mechanic or the "boss" of the dealership.
I have never damaged a car and have always been very carefull. It's all about trust basicly.
on a completely other side things can go wrong too. In brussels there's a big lamborghini dealership, and although I have done nothing wrong to them, they don't even allow me to go inside with a camera. The dealership only allows tourists to have a look, but absolutely no big camera's. They say it is a security issue and also desturbing to customers.
so you see, you just have to be lucky.
excuse me for my many spelling error's, i'm not that good at english but I try 
here you can see an example of some of the privately owned cars:
http://pj.snoobonline.com/IMG_3662.jpg
http://pj.snoobonline.com/IMG_0973.jpg