Zip codes are extremely convenient for finding places on a map. Just go to maps.yahoo.com and type in "pizza 90120" and you will find approximately 27,466 hits for places whose name contains the word pizza or have categories that contain the word pizza. That's definitely better than the 7,662,184 matches you find with just "pizza". You find that many online store locators will also take a zip code and find all of the stores within a given distance. Definitely useful.
For my first post here, I have decided to jump right into the concept of gazetteers. You can expect to see more posts on gazetteers in the near future as I plan to build one.
What is a gazetteer? According to wordnet it's "a geographical dictionary". Wikipedia calls it a "geographical directory" and has lots more to say about the history and the publicly available gazetteers.