macromedia has had a j2ee server jrun and some other java products. i was always expecting them to use flash as a frontend for j2ee apps (it was possible before but a little complicated). but this is purely revoltionary. flex sounds great but adoption by the community is important. it can be plugged into any application server. i hope to see the programming style soon.
i am not sure about rich internet applications (ria). are ria for a better web experience only based on browsers? and i read that microsoft might even remove the browser in favour of other thick clients.( http://weblogs.java.net/pub/wlg/648 )
so as a prospective developer i have no idea where the future is. how rich controls does a client want is the question. does he want to get out of the browser to a thick client? suprisingly i think java is winning this race. you have flex, and sun packages a thick client with the default sdk download.( http://java.sun.com/products/javawebstart/ ) another interesting view is that the future is peer 2 peer. here jxta has some headway.( http://jxta.org ) please compare any similar .net projects.
a java desktop is going to be released sometime. basically suse linux with a lot of sun apps like staroffice and lots of java integration. and its not free!!
so i guess ms is in for a good fight... who'll win lets see..
for the moment lets hope that we get time to learn atleast one api...