Based on a Deutsche Bank study, the article notes that countries with very small black economies (France, Austria, the Netherlands) and countries with very large ones (like Greece) suffered less from the recession than those (which apparently include Germany) with a medium-sized undeclared sector.

While the study and the article conclude that virtue is the better route out of Germany's current situation, it is still quite unexpected to see such praise of informal economies... unless you consider that the business press is desperate for arguments that make it possible to say the economy is doing better - and including the black economy is an easy way to boost statistics, surely...