- Many offline storage methods (appcache, localstorage, indexeddb, websql, chrome.storage).
- Many configurations (temporary, persistent, unlimitedStorage, quota API).
- Many browsers.
Nobody really seems to know how much space is available for which configuration.
Solution: A quota checker application that pushes the quotas to the limit (somewhat tricky for persistent & unlimitedStorage though, since we may clutter up the user's machine).