I was on the highway, driving along in the left lane, minding my own business. Speed limit is 75MPH, so moving along. I passed some slowpoke Jeep that was in my lane, doing about 50MPH. Traffic was heavy, so I stepped on it a bit getting around the Jeep (didn't want to hold the guy in the the lane to the right up), then hit the brakes when I cut back left, so I didn't run into the guy ahead of me. All I got was a woosh! The brake pedal went to the floor, and I may as well have tried stopping with my breath.
I downshifted (engine braking is illegal there, but better than an accident, I suppose), and worked my way to the right lane. It was another 10 miles to my exit, so hazards and minimum speeds it was. Since the area wasn't familiar to me, I worried about getting stopped for the exit. I managed to get through the exit, to a parking lot without incident.
This is the second booster that has done this to me. It was explained to me that one of the diaphragms fails. Doesn't help me stop any better.
If this happens to you, put the transmission in neutral when stepping on the brake. Stepping on the brake effectively creates a vacuum leak, which causes the engine to rev, which is counter-productive to stopping. The e-brake isn't much help.
Some Fiero guys here may have figured out my inconsistent braking problem: the calipers are frozen, or some such thing. Basically, when cold, the brakes are almost through the floor to get any braking, but when warm, the slightest touch will about put you through the windshield.