Third, think about what you are trying to accomplish with your map, and how your customers and partners will interact with your maps when they are done and eventually integrated into your site. Do you want to allow for user-generated updates, as Google has begun to do with their MapMaker site? Do you want people to use the Facebook Like button? Do you want to integrate with Facebook Places?
Fourth, understand the power of visualization. Warren's iPhone locator app, mentioned earlier, takes the longitude and latitude and time stamps in a database -- something that is almost meaningless to most of us -- and places dots on a map so you can see where your iPhone has travelled, which is much more meaningful, and potent.
Finally, a good place to keep track of the most current happenings is the O'Reilly Where 2.0 conference. The schedule from the 2010 edition of the conference, with links to the papers presented, will give you a sense of the state of the field. Good luck making your maps!