Some years ago, I has a 3/8" bolt stick in one of my tires. I noticed it and made a mental note to get it fixed ASAP, but, being a broke college student, ASAP meant 'next time I went home and borrowed money from dad'. Besides, the tire wasn't leaking air.
Fast forward a few days: I'm driving home - in my old full-sized blazer with 2.5" suspension lift and 33x12.50 tires - hardly the most stable thing ever to hit the highway - when the bolt finally came out. I don't know if I slung it out (~70 MPH) or if I wore the head off and the rest of the bolt pushed down into the tire, but either way, a large hole appeared in the tire almost instantly. That's probably as close to a sudden blowout as you're likely to experience at normal highway speeds, and, the point is, even with a large tire suddenly going flat, I was able to slow down, steer off the road, and get stopped without any real trouble.
The point, again, is that 'movie blowouts' - where you lose control of the car - are grossly exaggerated.