I do not think that we can use an IP address to individually identify a person, particularly in a legal persecutory context like that of the Yahoo v. France  case.

One issue is the introduction of protocols like 802.1x which are now used for wireless transmissions between computer systems.  Even though theoretically you could’ve sat inside France inches away from border and set up your box (containing a CPU, memory, hard disk and network card) in Germany, and use extension cables to use a monitor and keyboard a few feet away in France, this was very unrealistic for someone to actually do.  Wireless network devices take this scenario a step to a new level of reality in that you can actually be roaming a much further distance from your Access Point, and not physically connected to it.    This means you could be Standing inside Germany a number of yards away from the border and be connected to a wireless access point in France.  One could even use a wifi network across boarders by accident. And if you’re so inclined,  you can use something like a bi-directional parabolic antenna (14-20 dBi), you can be over a mile away from your access point.  Before the introduction of wifi and WANs, back when every computer on the internet was physically connected to it via ethernet or some similar medium, I feel it was much more fair and realistic to try to tie an IP to a human in a legal context.  Remember, we must be certain beyond reasonable doubt to convict.

Another problem with the complexity of our current infrastructure is a completely different subset of protocols / services which are essentially now universally used in consumer market products.  Protocols like DHCP which attempt to connect a computer to a network without their help, make tying an IP to a human much harder.  These systems make it so that every time you boot up your computer you will potentially receive a new IP address.  Even though there are methods of getting a reliable IP across boots (such as DHCP Reservation), these are not things that most users know about or have any reason to want.  I have DHCP Reservation disabled on my router.  I love DHCP and the ease-of-use it provides me on a day to day basis, I do not mean to sound critical of the protocol.  It is merely a good example for the argument against linking an IP address to a human being, or filtering content by looking up the country inside a whois record for every incoming connection.  Back when it was much more common for a computer to be configured to use a fixed static IP address, I feel it was much more fair and realistic to try to tie an IP to a human in a legal context.

The third issue is proxies, and other similar services which mask the IP address of the user.  However, these are things that people must consciously commit.  Accidentally connecting through a (foreign) proxy is not a common problem among people who haven’t configured their computers to use a proxy.  In this respect, I don’t feel that this adds much to my argument, but I still feel it’s an important aspect of this discussion.