I posted the following in February:

Now, in July, things are indeed a little clearer.

The 16 different states in Germany are sending out their letters at slightly different times. In Bavaria the first "invitation to register" went out at the end of May. The first reminder went out at the end of June. This is only to people who were never previously registered. Those who were previously registered in some way will have received their letters earlier. There will probably be a second reminder at the end of July. People are calling these three letters "Bettelbriefe", i.e. begging letters.

Although the second letter says that you are legally obliged to send them your information - "Sie sind gesetzlich verpflichtet, uns Auskunft zu geben" - the only "law" that obliges this is the Rundfunkbeitragsstaatsvertrag, which is basically the TV companies' contract with the government, it's not a proper law.

So you can safely ignore these three letters.

Next, if you don't register, you will be forcibly registered - i.e. "Zwangsmeldung" - using information that they assume to be correct, but which you haven't personally authorised. About two or three months after the third "Bettelbrief" they'll send you a bill - a "Beitragsbescheid" - according to this forced registration. It will be a bill for the months from 01.01.2013 plus a small late fee. It's at this point that you have to make a decision, one of the following:

1) Pay up, and then continue paying up every month for the rest of your life
2) Continue to ignore the letters
3) Within 30 days of receiving the Beitragsbescheid send a letter of contest (a "Widerspruch")

If you choose option 2 then they'll continue sending you further bills, and they'll add late fees as well. Eventually this could go to court and the money be stolen straight out of your bank account. But this can only happen once the owed amount exceeds