Update 2: The fact that this is dangerous, possibly deadly, and probably illegal is blindingly obvious, but several of my friends felt obliged to tell me so anyway. Don't try this at home, kids.
I was joking around with somebody about using one of these on a bicycle or skateboard to pull myself uphill using the San Francisco cable car cables.
The cable is 28 inches below the street surface and moves constantly at 9 mph. What's to keep somebody from hitching a ride by reaching down with something like this and grabbing the cable?
San Francisco being what it is, I'm sure somebody has already tried something like this.