Art and source photos aside, this link is sort of disappointing. For example,

>As Mars' diameter is about half of the Earths, the elevator cable wouldn't have to be as long to reach geostationary orbit and due to the lighter gravitational pull it wouldn't suffer as much stress from its weight.

Mars' diameter has nothing to do with the distance to stationary orbit, which is a result of gravity (and thus its mass).

The diameter actually does have an effect on where geostationary orbit is: it changes how fast the surface is spinning, and hence the orbital speed needed for a stationary orbit.

Mars spins once every 24 hours 37 minutes. If the diameter was twice as large, it would have to be moving twice as fast to maintain that length of day.

Interestingly, since you orbit faster the closer you are to the surface, a decreased diameter actually pushes geosynchronous out away from the planet. This effect is, of course, very much negated by the absence of mass. Still, two equally massive planets with the same rotational period but NOT the same diameter will have different geostationary altitudes.

I assumed he was thinking of mass as a function of diameter, which for a rocky planet makes sense to me. I thought his comments were pretty amazing myself!