I duno,  i think if you could fill the bottom one with a few feet of cement mgith be better.

You could do as the Dans have done with one particular tower (pipe of 1 ft or so diameter?) and make it a tilt-up tower; or you could use a bit larger pipe (2 ft or so diameter) and install the ladder inside.

Seems like much less windload to me, less material and cheaper. Safer. And less of an eyesore in the landscape as well.

For the 4000$ it takes to buy two containers, I think one should be able to purchase the steel pipe and be left with change.

If you should go with two stacked containers, I doubt whether 'normal' guy wire (steel wire of 3mm or so) would be enough to take the windload of an 80 ft high stack of containers...

You could calculate yourself easily the load the wind would put on that 'tower':

Fd = Cd * A * 1/2 * rho * v^2
where Fd = drag force of the wind (in Newton)
Cd= drag coefficient of the containers; I'd assume Cd=1
A= frontal area of the tower (projected area; the area that is exposed to the windforce)
rho = density of the air (1.2 kg/m^3)
v = windspeed, in meter per second

That force (Fd) exerts a moment on the 'tower' at 40 ft (midway).

I have actually been looking at it for a structure near my house, where you could make use of the enclosed part of the tower.  It could host large tank of water up high, that your water lines could run through. This would provide for water pressure even if power failure, or if your main water source is disconnected.  You could also run ducting up the tower and make a sort of stack, that could use Venturi effect (or if painted a dark color, solar power) to help ventilate a house or shop.

It could also act as a strong platform for large inefficient VAWTs.  One of the main drawbacks of VAWTs is getting a big, non-furling thing up in the air and keeping it there. Maybe this could help in certain situations.  A container will also have a nice 8'x8' platform on top that you could visit just to get a good view, or could hold a small array of solar panels.  

There are various structural items to take into consideration depending on your application and location. But for certain purposes, it seems like an interesting option.

A little to the side of the topic, here is a page with a lot of different shipping container architecture.  
http://www.fabprefab.com/fabfiles/containerbayhome.htm

Surely not, but are you the same Bozo I used to know that played a guitar and sang country western like Marty Robins and Johnny Cash etc... and told the stories about the songs????
Or some other Bozo. :)

Sorry, just a joke there, Your not a Bozo, but I did know a Rolling Thunder once about 8yrs ago.

Back on topic, some of those containers are nice and could be usefull for many things if you get them cheap enough delivered. I wanted some but shipping to me cost too much even though the containers where fairly cheap.

Bury one in ground and you got a mighty nice big storm shelter for the toranados!
 Maybe on blocks a nice workshop, 2 side by side and a roof over them for a doublewide and you got a nice auto shop? 1 could make a nice paint booth sealed off to itself.

As for stacking them end to end? Skyscrapers are mighty tall and don't blow over too easy, so it's a matter of doing things right. Might need to use several stacks braced for supporting each other, but then you got 3 towers or maybe 4 towers? If you put a wind genny on each corner of a container and had 4 stacks you would have 16 gennies all  about 8 feet apart, and I dought that would blow over as easy as one stack.
 Would you maybe like to sell power to the grid?

Hmm, also if you did something like that you could put rooms every 8-10' high for workshops or whatever. No reason to waste the inside space, make it pay for the containers also :)
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nothing to lose