A wheel-chair is an excellent way to get around when your legs don't work. I've never tried to get myself around without someone pushing me for any length of time... but the short periods I have experimented with prove that I need a little more arm strengthening exercise.
Crutches are an excellent way to get around too. The problem is that they still require input from your legs. After a distance (a not very long distance these days) my legs begin to give out. Aching, stiff and finally pain.
Enter my wheelie-walker. I can still walk supported (as with my crutches) but when I get tired and my legs give out I've got a seat right with me. On a bus, on a tube - or my favourite; when I take a walk and forget that I have to come back again.