A German court considered the IP address to be of the public domain. Parallel with "physical" world could support the decision: home address is public information unless one opts against it and forbid the name and address to appear in public directories.
there is however another parallel: the IP address is not your address but also the "image" of you on the internet. In that case can it either be private? Difficult to see.
THe whole debate has an incidence for crime: what is private can be stolen; what is public cannot be.
"German Court Rules That IP Addresses Are Not Personal Info" (21 October 2008)