I had my first experience tonight with the dreaded "high-speed wobble." It happened on a fast descent, in the most dangerous part (a long curve with lots of road hazards to avoid -- gravel patches, manhole covers sticking up a couple of inches above street level, etc.). Without warning the front wheel began to shimmy violently. My first instinct was to panic, as the bike was becoming very hard to control and I had visions of planting my face on the asphalt. However, I suddenly remembered advice I'd seen here on BF several times to remedy just this situation: "Grip the top tube between your knees." I did so, and instantly the bike became steady as a rock. I finished the rest of the descent smoothly without even having to slow down.
There's been lots of useful information that I've gleaned from BF in the past year, but this time, it saved me from what could have been a serious injury. This place is a great resource.