Does it mean "Use of static classes is wrong" (in which case the article is incorrect) or "Static classes are often found in badly written code" (in which case it's not saying that static classes in themselves are bad, but that they are sometimes used incorrectly)
Static functions are more efficient than non-static because you don't need to create an instance of an object to use them or pass a 'this' pointer into method calls.
Use of static classes to hold global variables is a different matter - in which case the underlying rule is not that "statics are bad", but "globals are bad".
