jQTouch is a jQuery plugin for developing mobile web apps.
It takes an HTML page with several sections, and creates a view for each div. The main view is the div with id "#home".
Now that most recent browsers support HTML5's localStorage (a local key-value store), it's possible to have a settings page for a web app that doesn't require users to sign in: their settings are stored locally.
This data can be erased, though, if the user clears the temporary data stored by their browser - similar to cookies.
HTML5's client-side SQL databases allow data to be stored more permanently (until the databases are erased), but aren't yet supported by all browsers (Safari & Chrome, but not Firefox).
This example web app, using jQTouch in the client and PHP on the server, provides settings which are stored in a client-side database if available, or localStorage otherwise. Add a feed URL and it should be remembered next time you visit the app.
The code is in GitHub. There's not much documentation, but feel free to add jQTouch, edit config.php and app.specific.js and make it do interesting things.