Why a widget? From Chris Bowley
With backstage running a Widget Competition, there has never been a better time to get into writing widgets. But the chance of winning 'a well known media player' should not be the only reason why you want to create a widget!
In the last few months I have written a couple of Yahoo! widgets: a what's on widget to demonstrate the prototype BBC schedule API and a widget allowing you to update your Last.fm profile as you listen to the radio.
One of the main reasons why these projects were developed as widgets is that they allow you to make client-side cross-domain XMLHttpRequest calls. The Last.fm widget makes calls to two different domains and therefore cannot be hosted as a web page. Widgets can also make calls to control installed applications, such as streaming audio through Real Player, and display OS information such as laptop battery life or WLAN coverage. In essence widgets provide a sandbox with fewer restrictions than web browsers but they do have their disadvantages.
Overall I think widgets are a good alternative to web pages and traditional applications, but you should only develop one if the circumstances don't allow the same operations to be carried out in a web page or if a widget will provide a better user experience.