You have an idea for the next online service that will change the world. Good! Now, should you make it accessible through a web browser, or will you create a desktop application to provide a more responsive and user friendly user interface? Think Google Maps versus Google Earth.
If you are targeting people using a PC or Mac, in most cases you will choose to make your application browser accessible: you will create a web application. However if you are targeting mobile devices, the temptation to create an application that runs on the phone will be greater. With a mobile application, you can fully leverage the capabilities of the phone and provide the best user experience, or at least so goes the theory. In practice, you will have to support a zillion different phones and most people just won't know how to install your application on their phone. For those reasons, I think the appeal of web applications is even greater on mobile devices. But there are right now two limiting factors: the hardware and the software. I am not worried about the hardware: there is a fierce competition in that market and mobile phones are getting better every day.
But what about the software? Smart phone can in general run Opera for Mobile, but what about the so-called feature phones, which represent the bulk of the market? A few days ago, Opera got us closer to making web applications run smoothly on most phones with the release of Opera Mini. It has already been called by some as the "best mobile application to date". It runs on virtually any phone (check if your phone is supported) and runs beautifully (give it a try!). Today Opera got us closer to making web applications really usable on mobile devices.