Tzakuk - 11:16 pm on Jun 7, 2012 (gmt 0)
Really, it depends on what you are trying to do. If you are planning to keep a database of your visitors' information, or if you want to populate data fields with specific information based on the input in other fields (e.g. populate city and state based on zipcode), then php/MySQL is surely the way to go.
If you are just providing pre-populated fields for returning visitors' convenience, it is simple enough to add a check box or radio button; ask if they would like their information saved, and point out that cookies must be enabled. Voila!