In theory private websites do not need an impressum (§55 RStV). The legal situation is not very clear though. This page: http://www.homepage-impressum.de/ (german) does discuss the problem quite extensively but to sum it up:
Directly defined are three categories of websites:
a) purely private sides. -> They do not need an impressum.
b) professional "opinion-leading" page (read: anything remotedly similar to a newspaper) -> They do need an impressum.
c) businesslike sites -> They do need an impressum.
Obviously there is a 4th category: Everything which is not a, b or c. It's a grey area and the contentious jurisdiction is ambigious. A site probably falls under "businesslike site", if it's a service which is "usually" done for money, it's not relevant if someone actually gets money for it. As it is relevant for competition law (and _not_ criminal law) it's relevant if it effects "the market". One can only be sued by a competitor who can claim to be effected by the site. So probably most sites won't get a problem without an impressum but to be safe the link and most people would advise to make an impressum. It's important to note that most cases regarding impressum are not even brought to case, usually a lawyer sents a "warning" with a claim for some degree of money which mostly consists of the "expenses" of the lawyer...
Of what an impressum in germany has to be made of depends (discussed in detail here http://www.homepage-impressum.de/abm...ein-impressum/ (german)). If one is only in the grey area of §55 RSTV (so neither of the 3 groups), it's probably enough just to use one name and adress. There is § 5 TMG I which defines the necessary impressum for a businesslike site. To use them is the safest.
- Name and an address at which the provider is operating (provider being the provider/owner of the site, not a provider like "telecom"); if the owner is an artificial/legal person, the name and address of the authorized representative.
- Statements, that make possible a fast electronic contact-reception and immediate communication with them, including the adress of the the electronic post. According to most court decisions one also needs either a telephone number or a contact form which theoratically allows for an answer in less than 60 minutes (Note contact form alone is NOT enough, you need to mention the e-mail directly too)
- If the official juristical person of the site is registered in a register, which is somehow related to what the site is offering, one also need to to write the register number in the impressum
This is in no way any kind of legal advice (necessary disclaimer in germany not to be sued ;-)).