Viewing Facebook photos is really great in this app. They have implemented the same "flick" style of navigation that the iPhone uses and photos flip over to reveal comments. Overall, the UI is pretty intuitive and uses a lot of the same conventions that Apple does. Taking photos and uploading them to Facebook could not be simpler. Just tap the camera icon, take the picture, and tap to upload.
The installed application is a great improvement over the previously released web based version, which does not offer as high a level of functionality or as fluid of an interface. While I was initially skeptical as to the benefits to a standalone Facebook application, as opposed to just using the web based one, features like photo uploading and chat justify its existence.
Facebook has built an extremely slick iPhone application. My first impressions are extremely positive and Facebook has definitely earned a spot on my first page of icons. Its navigation is very fluid and the feature set is complete and easy to use. It was important for Facebook to have an application at launch for the iPhone App Store, with competition coming from a variety of other social networks, MySpace included, so it's good to see them bring such a solid offering to the table.