JavaFX

Moving more 'logic' to the client seems like a good idea, but doing it all in Javascript/AJAX is quite the hassle.

Flex is *really* cool, but you won't be able to re-use any existing libraries for, for instance, parsing accessing caldav calendars.

Silverlight, even with Mono present, is too Windows-centric to my taste.

JavaFX seems old-fashioned, but being able to re-use general-purpose libraries is compelling.

[edit] Getting the SDK for Linux

Unfortunately, the SDK is not yet available for Linux, though people have been reporting success using the Mac version of the SDK.

Getting the mac version is a hassle though. The technique mentioned at http://www.weiqigao.com/blog/2008/12/04/using_javafx_1_0_on_linux.html no longer seems to work for JavaFX 1.1.1. Instead, download the netbeans zip from http://updates.netbeans.org/netbeans/updates/6.5/uc/final/stable/patch3/javafx2/ (play with the url for newer versions :) ), unzip it, and you will find the SDK in 'netbeans/javafx-sdk'. Be sure to 'chmod a+x' the bin directory.

Nice documentation about javafx and maven: http://blog.nelsonsilva.eu/2008/10/10/javafx-maven-on-ubuntu/ . Note that the locations of jars have been changed a bit since.

Unfortunately, the plugin is producing the same error as mentioned on the mailinglist: http://sourceforge.net/mailarchive/message.php?msg_name=496339FC.9050803%40gmail.com

The ant tasks that come with the example projects in the sdk work fine.