I started a new blog dealing with external obsolescence on Blogspot at http://externalobsolescence.blogspot.com/
The Dictionary of Real Estate Appraisal defines external obsolescence as: "An element of accrued depreciation; a defect, usually incurable, caused by negative influences outside a site."
External obsolescence causes a loss in value to your property caused by forces that you can not control like the current condition of the world economy. That's what it means when its says "usually incurable", you cant fix it and just have to live with it.
The type of external I will deal with in the blog is "Locational Obsolescence" in other words a bad location. This is another thing you can't fix, if you buy a bad location, you are stuck with a bad location.
In my travels as a real estate appraiser I find some real good examples of bad locations. It should be noted that none of the examples shown in the blog are any of my clients property.
So check out the External Obsolescence blog