Whilst the article was very good, I would like to issue a note of caution; even if the address does not appear to be that of a DHCP pool used by an ISP, the results may still be misleading as:

1) The traffic is routed via the company WAN to a quite different address - in an extreme case I have seen this give my address as being the United States whilst I was in England.

2) The address is that of the failities management company rather then the actual address. Again I have seen this give an address in Germany whereas I was definitly in the UK.