A lot of people are asking for Apps these days. They have become trendy.
I’m using the term “app’ to refer to an application that runs on a mobile device, most often on iPhone (and iPad), but also on Android (Samsung) and Blackberry devices. They are available for download from stores and work only on the device they are developed for. Some of these apps can do amazing things, and transform the device. Check out animoog –  http://www.moogmusic.com/products/apps/animoog-0 – no wonder apps are considered cool!
When a client comes requesting an app, it often emerges that they are looking for a tool that allows efficient mobile access to information. While a app can certainly do that, and there are lots of apps that do, it may be possible to deliver the desired solution with a web app – a mobile-oriented web application. These run on a mobile web browser – iPhone AND Android, etc –  and do not need to be downloaded to the device. A web app is likely less costly to develop than a true app. On an iPhone, users can even drop an icon to launch the web app, resulting in an app-like user experience. For some examples of web apps see http://www.jqmgallery.com/
There are limitations. Much of the power of true apps comes from being able to integrate phone, audio, gravity sensing, camera/video, gps location etc. Also, there is appeal to have a marketplace – the app store – from which to distribute the tool. An app can theoretically work when there is no Internet, unlike web app, but this distinction blurs in practice. While apps are available from the device-specific app stores, you can release a simple launcher in an app store, which loads a web app in the device.
In some circumstances, an app is truly the best technology for the solution, but if a web app is appropriate, it offers significant advantages. If you are looking for a business solution that involves a mobile interface, I recommended keeping an open mind to the possible benefits of the simpler web app.