After attending the Devoxx 2009 conference in Antwerp this year and seeing a number of presentations on JavaFX I got motivated for using it. The main reasons for looking at it would be: 

• it runs on the JVM so integrates nicely with other features/libraries in Java. For mobile it is based on MIDP which is available on many devices. 
• it is a really compact expressive declarative syntax for user interfaces which is attractive
• both desktop and mobile clients can share most of the code. Simple applications can be deployed with minimal modification on both desktops and mobiles.