Admittedly, the german language neither is an easy to learn nor an elegant language. During my stay in Kaufungen, I found this »Berliner« ad in front of a bakery. The writer obviously was not a native speaker (instead of »verschiedene Fühlungen« he meant »verschiedenen Füllungen«, »various fillings«):
In his column, Bastian Sick collected some (even user contributed) material concerning german grammar. As the column got very popular, he condensed the material in a series of books (currently three) called »Der Dativ ist dem Genitiv sein Tod«. There’s even a »three in one« issue.
If you have to cope with the german language (e.g. being a technical writer etc.) it will help you to avoid common mistakes and improve your skills. Even if you are a native speaker :) .