This goes a lot deeper than the article seems to suggest. There was an quiz on spiegel a while back that went in depth into the hidden meanings that only HR experts can extract from these letters (http://www.spiegel.de/unispiegel/jobundberuf/arbeitszeugnis-...). My wife who works in HR managed to get them all correct, but I would have missed a lot of the explicit meanings inside the numerous formulations.

In general these letters can state things such as:

1. this person has no manners

2. the person is an alcoholic

3. the person is an arrogant diva, etc

Some more for those who can read German (http://karrierebibel.de/arbeitszeugnis-formulierungen-bewert...)

As someone who has worked in both the US and German systems though, I actually prefer the German one for the reasons pgeorgi mentions - its like having a certificate that proves what you did and how well you did it after you complete any job, then regardless of whatever happens to an employer (they could go bankrupt, your boss could leave, etc) you still have that certificate that proves you did what you say you did.