How do advertisers and websites know info about me? I get more and
more geographically specific adds, like 'meet single women in san
diego!' (which is where i live). Also, for ex., when I go to look at
pbs.org(?) under t.v. listings, it automatically takes me to the san
diego listings. How do these sites and adds know where I live? What
else do they know about me?

The short answer: magic.

The long answer:
If you know a little about TCP/IP, or more simply, internet addresses,
you will know that each computer connected to the internet has an
address that identifies the computer and location you are connecting
from. (Sometimes one address will be shared amongst several
computers.) You can find out your host name and IP address using one
of these websites:

http://www.sinc.sunysb.edu/cgi-bin/MyIP
http://www.myip.dk/

(search terms: "my ip")

A hostname doesn't always exist, but an IP always does. (Hint: a
hostname can be words, letters and numbers, whereas an IP address is
only numbers.) Sometimes, the hostname will give away your location,
for example, user101-chicago.fakeisp.com. Other times, it will be less
obvious from the hostname, for example just user101.myisp.com. By
navigating to the ISP's website (www.fakeisp.com) you can find out a
lot about a user's location. And if all else fails, for instance, a
host name doesn't exist, one can look up an IP address and find out
meaningful information about it from a site like this:

http://www.arin.net/whois/

(search terms: "reverse ip lookup")

The websites you navigate do something similar to this, but they have
a program written to target ads to you, and it will look up your
location automatically. Perhaps, it will see your IP address follows a
pattern, perhaps the website will assume all IP addresses beginning
with 10.10 are based out of Chicago, for example. Your internet
address says a lot about your location. Try looking yourself up, and
you'd be surprised what you can find. When I look my own address up, I
not only see my city, but the name of my neighborhood.

If this worries you, there are several ways of browsing through a
"proxy" server . The proxy server will know where you are browsing
from, but the sites you browse will think you're accessing it from the
proxy computer. Such sites are popular amongst privacy advocates, but
are also scrutinized as it can possibly aid in committing Internet
crime. The most popular one is "Anonymizer", but they have recently
begun charging for their service. A free one is:

http://www.the-cloak.com/

(search terms: "anonymous web browsing")

I hope you understand more now.