I don't understand people bitching about Impressum like its some sort of German-only thing.
I am sure if you looked at the legislation of many countries, you would find similar requirements for companies to identify themselves. Off the top of my head you have Austria, France, Italy, Spain, Switzerland, UK ... and probably the rest of the EU/EEA states as well. IIRC it is also a requirement in a number of Asian countries.
In reality requiring an Impressum (or equivalent in other countries) is no different to having to put identification information on a company's old-school letterhead. Its just good manners so that your customers/suppliers can know who they are dealing with.
Personally I dislike the US attitude of trying your damnest to hide any trace of your company's identifying or contact information from your website. ;)