I did register, I believe online, with the Munich office a few years ago, and gave them my e-mail as well as my address. I haven't gotten one in awhile, but they used to send me "messages for US citizens", with such useful advice as the following, received in an e-mail in September 2004:
"Terrorist actions may include, but are not limited to, suicide operations, assassinations, hijackings, bombings or kidnappings. These may involve aviation and other transportation and maritime interests. Terrorists do not distinguish between official and civilian targets. These may include facilities where U.S. citizens and other foreigners congregate or visit, including residential areas, business offices, clubs, restaurants, places of worship, schools, hotels and public areas. U.S. citizens are encouraged to maintain a high level of vigilance and to take appropriate steps to increase their security awareness."
I also sometimes get information about help with filing US taxes.
But I never got invited to any barbeques, either.