Just had my first Ti iPhone app approved. It's very simple at the moment - maps your Facebook checkins so you can see your friends on a map, though the next update will have some more useful additions.

The biggest challenge was getting the new Facebook Graph API working in Titanium alongside Ti.Facebook because it uses the old REST API client.

Thanks to everyone who helped out getting started with Titanium.

iTunes link to the app:
http://itunes.apple.com/gb/app/checkins/id396409407?mt=8

Edit:

Facebook integration info:

In order to use the Graph API I had to use a Ti.Network.HTTPClient to make get and post requests. That was easy enough. At first I created the entire app using just the HTTPClient, using the desktop authentication method described here: http://developers.facebook.com/docs/authentication/desktop.

You can also use the normal web authentication described here:
http://developers.facebook.com/docs/authentication/

To do this you need to use a Ti.UI.WebView because this is how the user enters their username and password.

You need to subscribe to 'load' events on the WebView, and check the URL whenever it changes. When the URL matches the end point (depends on the application and the authentication method used), you can get the access token and append it to your Graph API requets.

That worked fine for me, but Facebook doesn't seem to provide a way to easily log out a user; which makes it difficult for someone else to use the app with their own data. In some situations that might be fine, but I wanted to allow 'guests' to login on a friends phone.

So, I used the normal Ti.Facebook login button to start and end sessions. Once the user is logged in, you can exchange their Facebook session for an access token:

See 'Exchange session key for an access token' here:
http://developers.facebook.com/docs/authentication/

Hope that helps