I had the joy of getting my first flat tire in my E46 328i sport the other day. It happend on the wonderful Los Angeles freeway system.
I was going about 75-80 MPH along 10 eastbound from PCH when I must have hit something. I don't remember hitting anything, but shortly after that, the car started vibrating. It was minor at first, so much so that I though it was just the road surface I was feeling through the sports suspension. As I turned onto the 405 southbound, the vibration got steadily worse. I began to suspect a tire or wheel problem, so I relaxed my grip on the steering wheel slightly to see of the car was pulling to one side or the other.
Nothing. Just vibration.
I decided to pull over to check it out. The vibration was getting more intense, and things inside the dash began to resonate. I finally found a safe spot to pull over, and check the tires. The right rear was destroyed. The sidewall was blown out in multiple places, but was still on the wheel. Changing the tire on this car was easier than any other I've had to do, and you just can't beat having a full-size spare!
As I put the bad wheel into the trunk, I noticed that the inner side of the wheel had quite a number of little dents in it. These dents would later cost me several hundred dollars in the form of a new wheel. 8-(
I suppose it would have been more noticable if one of the front tires had gone, but now I see that one of those tire pressure monitoring systems would be worth it. The 17" sport wheel lists for more than $400. (Dealer cost is closer to $280, but they've got to finance their holiday parties somehow. 8-))
So, in summary:
Good news: If one of your rear tires goes at 75+ MPH, the car is probably not going to launch itself into the nearest ditch. I don't know about the front tires, and I don't plan on finding out.
Bad news: If you don't notice the resulting vibration in time, you get to buy a new $400 wheel in addition to a new $179 tire.
Be careful out there.....