Yes, I remember the plastic seatpost. I had one on my Colnago Super a brief time in the 1970s--before it sheared off and almost left me childless! I also nominate the nylon headset that was available at that time.
Speaking of Hi-E hubs, I also had a bad experience during a training ride when the spokes started breaking one after another on the front wheel . I barely made it home with about half the spokes in the front wheel remaining. I don't think it was due to my weight at the time since I was all of about 120 lbs. My advice: display only!
Stephen Bryne
Windy and cool in Fairfax, CA