Chris and Yurek,

You are almlost right.  It will, in fact, be that well known derivative of the sling, the trebuchet, that becomes the prefered mode of transportation in the future.  This is because of the great mechanical advantage it has over the human powered sling.

In fact, while up late one night, I saw something on TV about a fellow who threw his wife with a trebuchet.  She landed on a net similar to that used by trapeze artists.  Great landing.  Except for the bounce, that is.  She bounced right out and fell about 12 ft or more to the ground.  Broke all sorts of stuff.

Alas, it is true that all new modes of transportation have to go thru the trial and error and death stages.

jeff <><