To me it was when the episode ended with Picard having been assimilated by the borg. When I was watching it it was way too late, and I had a flight that I needed to catch in the morning. I pulled an all nighter because I needed to see what happened next, despite knowing that the next 24 hours would be spent in transit.

To this day, Picard turning towards the camera all borg'ed up right before the end credits is the biggest cliffhanger I've ever seen.