Okay, here we go again. Any IP cannot be used to identify an individual. It is not a fingerprint or DNA. It is simply the address someone was using at the point in time it is logged.

The courts here in Denmark have already thrown out cases with this very argument – it is impossible to prove who was using an IP at any given time. In this case an open access point was involved, but there are other ways an IP can be shared, intentionally or otherwise. Here’s a run-down:

1) Open wireless access.
2) Shared connections Who in the family did the evil deed?
3) Cabled thieves. Outsiders spliced into the network (and later disconnected).
4) Wireless thieves. An unauthorized wireless access point added to the network (and later removed).
5) Hacked closed wireless access. WEP is easy but WPA can be hacked too.
6) Incorrect logging at the ISP.

There are possibly more but these are the obvious ones. Yes, I know of cases involving each. It is in other words completely impossible to reliably know which PERSON was using the IP at the time of any transgression and you need for evidence to point to a person in order to prosecute. No matter who you pick there will be a huge doubt, making it impossible to convict.