According to a German court it is. (via Eric Fitzgerald's blog)
The remedy that this ruling implies - not logging IP addresses to a web site beyond the duration of the user's session - is either unsustainable or crippling to site security.
If it becomes standard practice in Germany to not log IP addresses anywhere for any length of time, they will essentially be declaring open season on themselves. There will be no network evidence trail and therefore no case to prosecute. I can't imagine it'll come to that, but it is interesting to ponder.