The seventies would be just about right, that was when I discovered an old Heathkit scope in the Physics lab at school (and the rest is history). What you are looking at is the phase difference between the signals on the X and Y plates of the scope so here are some more things you can try:
1) Different combinations of waveform, two square waves will for example trace out the sides of a square on the screen as they interact. Sawtooth waveforms don't work too well though because then you just have a conventional scope
2) Comparing two frequencies. If the two frequencies have a harmonic relationship then the pattern will be still and this is a great way of comparing frequency differences. If your pattern rotates once a second then you have a 1Hz difference between your two signals.
3) Phasing effects in music show up really well if you feed the left channel into the X input and the right channel into the Y input.
4) Finally, the advanced stuff.
O0