Rich Application Platforms
Well, there's been a bit of a kerfuffle about whether or not Silverlight (nee WPF/E) supports binding, widgets and XMLHttpRequest gubbins. And Adobe has open sourced Flex, as well as having had its Apollo platform out for a bit now. XULRunner is still going, being used for SongBird and Joost, and freshly the DVD version of Wikipedia, though whether or not Mozilla is promoting it well as a platform is under discussion.
Having done an awful lot of XULRunner programming in the last few months, there's still a lot to be done before its an easy to use platform. Quite a lot of undocumented interactions cause crashes - particularly race conditions between XBL bindings being attached and scripts in the body of the document being run, and any manipulation of the tree in script during an XBL constructor. But I don't have any idea how well Silverlight or Apollo handle such things, or even if they support anything as flexible as XBL. There needs to be an XULRunner 2.0 that is a lot more predictable in its behaviour, and less arcane in its invocations.