I'm not an expert. You can tell that because you are not paying me big bucks for this answer. 
The Computer Address you are thinking of is the IP address. And yes, everyone out there running a website can see your IP and also the info about your ISP (the company that sells you your internet access). The website has to have that info to talk back and forth to you when you click on links and to show you the pages.
The IP address and the ISP info doesn't tell the website anything about "You" personally - just how to talk to you. So the only thing that a website knows about you is what you tell them, really. If you are filling out surveys, then you can assume that any information you give them in the survey will be stored in a computer (and later sold to the highest bidder 
). Which is why, even though I just know all of you folks are lovely people, I do not give out my real name, address, and credit card number on these boards. When I buy things online (which I do often), I use either paypal or a special credit card with a very low $$ limit. You have to protect your personal info all the time. But that's off the subject.
There's a really good article with minimal techno-speak about the topic of IP addresses and physical location. Bottom line, though, is that they know what you tell them. And ppl are usually too trusting.
http://ezinearticles.com/?Does-IP-Address-Reveal-My-Physical-Location?&id=94220
