andyson,
I don't disagree at all with the fact that it is a very low level initial preventative measure. I think we just have a different opinion of how practical of a measure it can be. I am probably looking at it from a much larger scale perspective than you are, no harm there. For smaller mom and pop threads it can be a good tier 1 tool, beyond that, I don't think so. Certainly not here in a Global setting. That was the original question that you posed, why I didn't think IP mapping was a consideration for WGT to use, remember? They are a global company when it comes to IP mapping, no questions about it.
I'm not exaggerating anything for effect. IP leases are a common thing, as well as IP pools that ISP utilize. Anyone with a dynamic IP changes IP address every time they shut down and restart a modem. Many do this daily without ever knowing they have changed IP addresses. Automatic IP configuration settings are default on any windows machine, and it takes a bit of knowledge to assign a static IP even locally, much less externally. Throw in routers, hubs, switches, and wireless modems that all have unique IP addresses (that can be easily changed!) and the capability is multiplied endlessly. No exaggerations needed to make this point.
I will however take issue with your data collection methods. You are using this example as being efficient in blocking multi account sign-ups, yet use no other means (or at least have stated no other means) of verification, other than a comparison of a users linguistics? Not a good way to moderate a forum, and certainly no way to support an argument, no matter how small the community you used the techniques within. If you think users that are willing to manipulate rules in order to re-register are not going to adapt a posting style to aid in their discreetness, you are sadly mistaken. There are many fool proof ways to verify identity, depending in the application or venue, it's all a matter of how successful you want to be, and at what cost.
Are you at least able to see the difference between a small forum and a global forum as far as the potential damages that IP blocking can create?