This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
Not sure what you have in mind, but it's generally used more for user and application preferences, not fro actual application data. E.g., on Windows it's backed by the Registry, which should give you an idea of what it's used for.