Linking to your Dropbox account from your profile will put every bin as a full HTML file in your Dropbox
Apps/jsbin directory. This means you have a complete offline backup of your bins or any bin you edit.
Note that only the latest revision is saved to your Dropbox (though we're considering adding support for revisions).
You can see the simplicity of the Dropbox link in action below:
Finally, two way syncing is being investigated and will be released to Pro users if possible.