Answer: a mightily screwed up headset can certainly make the bike dangerous and unridable at speed and in curves, however, the reality is that headsets almost never fail dramatically *anymore*, at least not modern headsets. This post describes an incident 21 years ago (1989). In 1989 cheap headsets were loose bearing models with caged ball bearings. A blown cage could bend into the races and sieze a headset rather quickly. The replacement with a roller bearing headset (almost certainly a Stronglight A9, or perhaps a Miche) was a good move and has lasted 21 years. The reality is that even the cane creek S3 is far superior to any of the headsets available in 1989. The "one time cost done right" need not be more than 30 bucks or so.