I rode a segway, and I almost got flipped off of it because of PIO. That's right, ladies, the same thing that has killed many-a-testpilot can happen on a Segway. I leaned forward, then lost my courage and leaned back as it began to adjust for my leaning forward. When it shifted back, I lost my balance and leaned forward again, it responded, etc. The pilot induced oscillations got worse and worse (over a period of 2 or so seconds) before I got it under control by relaxing.