I've just read a posting on a discussion board that says your PC's IP address can be accessed to find out your home address. Jessica James
This may be true if you work for a government intelligence service, but it's not a simple process. When you go on the net, your PC is assigned an IP (Internet Protocol) address, which is made up of numbers separated by dots (eg 184.108.40.206). You can enter this into a "reverse lookup" service -- there's one at zoneedit.com/lookup.html -- and find out who owns it. In my example, the answer is Google, and the lookup provides a postal address in Mountain View, California. However, in most cases, the number will be one of a large block assigned to an internet service provider (ISP) such as BT, and knowing BT's address is not much help. You would need to look up BT's logs to find out who was using a particular IP address at a particular time, then look up BT's customer records to find the user's postal address. ISP's don't make this sort of information generally available.
If you buy a domain name, such as jessicajames.co.uk, then your name and address and other contact details will usually be listed in the DNS records. In this case, you just need to look up the domain name using a Whois service. But because many ordinary people now buy domain names for personal use, Nominet, the UK registrar, has changed the rules so that "non-trading individuals" can opt out of having their details displayed. (The owner of jessicajames. co.uk has opted to do this.)
If you want to keep these details private, you have to ask the agent who registered your domain name to modify the domain name record.
Backchat: A reader who is ex-directory was "horrified" this answer. She had bought a .net domain and says: "I find that you cannot opt out of .net addresses, only from .uk ones." Nominet does not, of course, control top level domains such as .com, .net and .org, or other countries' domains such as .it (Italy), .tv (Tuvalu) and .to (Tonga).
Lewis Peake says "just enter dummy details". Reading Whois entries shows that many people do.