I received this question from a client via email this morning and thought I would pass on the information -- Douglas
Any user ID or password that is stored and automatically retrieved is prone to be forgotten. I run into this with many clients and their Apple IDs. This is the login used to verify you own music, books and apps from the Apple store and is being used more and more for other services, too, such as Find My iPhone, iCloud and changing your Mac admin password.
If you have forgotten your Apple ID, don't despair, visit this page, "Apple ID Support " and it will step you through a series of processes to recover both the ID itself and help you reset the password.
Most other web sites will allow you to do something similar, when needed.
Link: Apple ID Support Page