I just think this is neat. I have no current plans to build or buy one.
There is a glut of standard shipping containers in the US because we import more than we export. You can often find these containers at around $1800 each, both 20' and 40' sizes. McKinney in Seattle will even customize them for you.
Lots of container housing projects.
Global Portable Buildings sell prebuilt human habitable cargo containers; one newsclip I saw suggested they go for under $8000. Hookup power/water/waste and live!
An expandable container 'house'
quux's mexican jumping wiki 
You may be interested in the Ace modular building units which can be used as a standalone unit or component of a larger structure. It is compact for transportation and storage, easily assembled/dissassembled with hand tools on site, and can be configured (both interior space and exterior windows/doors) for many applications. Go to www.aceamericas.com
i'm interested, but two questions:
1) are these acually ISO shipping containers (ISBU's)?
2) are you a member of the ISBU Association?
1) For the links on this page, I think so, but peruse the links for confirmation. The Ace units do not look to be tandard shipping units, though 'built to same dimensions'
2) no
the isbu is b.s. - its a bunch of container salesman trying to lather up their resumes with all these letters. who else is a member of the isbu besides the owners of isbu? what a bunch of baloney. McKinney and Global Portable projects are good
Let's see, you criticize a legit trade organization (ISBA) then tell us to buy from the two companies in your post. mmm, you are either selling advertising or you are a shipping container salesman for one of the companies you plug.