I thought I would throw this out there in case anyone has experienced this or might in the future. Several years ago, I was descending a hill for the first time on a fairly new bike and at about 30 mph, the front end started shimmying from side-to-side. Application of the brakes only made it worse. Very scarey. After that, it seemed to be doing it on just about every hill, and I was getting very nervous whenever I would approach a descent. I thought it might be the wheels, so I swapped with a similar set from my LBS and tried the same hill. Still the same problem. I thought maybe it was some flexure between the handlebars and the frame, so I swapped stems. Same problem. The best thing I found to reduce the shimmy, but by no means eliminate it, was lowering my tire pressure. Therefore, I began to think it was due to a frame misalignment or lateral flexure in the frame. Soon after that, my bottom bracket separated from the carbon frame, and I upgraded frames with the warrenty credit. New frame did the same. Rode it for a year or so, just taking it easy on the descents, but it was still unpredictable when I would have this problem, and when I wouldn't. Got a new frame from a totally different company, and it still would sometimes do it. Getting very frustrated by this point. However, I figured out what I was doing wrong. Yes, it was me, not the frame or components. I realized when I made sure my front QR skewer was very tight, there is absolutely no problem at all. I guess I just wasn't getting it snug enough and that was allowing lateral motion of the wheel. Since discovering this, my confidence is back, and I'm usually leading on the descents instead of dragging in the back. Hope this never happens to any of you, but if so, tighten your skewer up and try the hill again.