However, most people don't like to give a name and password every time they go to a site, so often a cookie is the best option for associating a profile with a user. Sites collecting information must find a way to integrate their profile database with their ad management system, so that the ad server can use the information appropriately to deliver the targeted advertising. Believe it or not, some sites collect a zip code during registration, but may use IP targeting to serve ads geographically. This is because, for whatever reason, they haven't yet set up their ad management system to take advantage of their user profiles. If you are planning a campaign, never assume that collected information gets used to target ads.
Profile targeting via registration information can be very powerful.
Collecting zip codes from users can allow for geographic targeting to a very small area with near-absolute accuracy, unlike IP targeting. For the most part, the only inaccuracies in a registration-based database stem from exaggerations or outright untruthfulness on the part of the users submitting the information. Take a look above at some of the information that sites tend to collect. A few of the questions can be used to target someone in much the same way as you might set a buying target in traditional media. Many traditional advertisers use gender and age in their buying target, possibly with some qualifiers like education level and income.