I know what you're thinking, an interior designer writing about living walls doesn't make much sense, but I am doing so not because I'm claiming to be an expert, but simply because it fascinates me. I came across this post in my daily blog research through www.notcot.org (check it out if you're not familiar, it organizes thousands of different blogs into one convenient package) http://www.inhabitat.com/2009/11/23/living-green-wall-buffers-filters-construction-zones/ and although it is conceptual, I think it addresses a significant design opportunity that no one ever takes, and also provides a living breathing environment for pedestrians near construction zones.
Most people reading this are probably only familiar with living walls in exterior settings, but there are several examples of successful interior living walls (the Sydney International Airport is shown below). I myself have tried convincing clients of the benefits of creating interior living walls instead of using the typical disposable plant service or the dreaded fake fig trees most commercial clients pay for, but the issue always comes down to lack of light, expensive watering systems, and simple lack of knowledge and experience in the Denver area to deal with keeping these things alive.
There are also so many of us out there with a 'black' thumb who couldn't keep a cactus alive (like me), that convincing clients to take a leap to something this exotic is a scary prospect even for a designer or architect. I have come across companies like this http://www.eltlivingwalls.com/ that provide pre-grown modular systems specifically designed for each unique ecosystem, or self-watering systems such as these http://www.inhabitat.com/2009/05/21/greenworks-felted-living-wall-system/ that make the issue of maintenance almost non-existent.

One of the most unique and simple systems for creating your own living wall almost anywhere is the Wooly Pocket system http://www.woollypocket.com/. The product is made of recycled soda bottles and you just hang them, insert your choice of plant, and water as needed.
And finally, yes there are high profile installations that have failed, but intelligent designers everywhere are finding ways around common issues that plague the living wall. Check out this site for stories of lessons learned regarding the living wall. http://www.treehugger.com/files/2009/08/rip-londons-first-living-wall.php
David Key - Jan '09