I arrived about an hour late at JavaPolis thanks to some impressive traffic jam on the way to Antwerp but am glad I did manage to catch most of Sang Shin's "Introduction to AJAX". He discussed several frameworks and did a demo for each -- from Dojo through jMaki and DWR (Direct Web Remoting) to GWT (Google Web Toolkit).
After lunch I attended Dick Wall's "Google API's" session which was another eye opener. Unfortunately he didn't talk about OpenSocial as it said in the schedule but he did give a great overview of some insanely cool functionality in the Google Collections Library (BiMap, MultiMap, ReferenceMap, Constraints,...). I really need to read up on this and see how it applies to my Flex development and if there are any similar implementations out there.
The second part of his session covered the Google Data APIs, another great project and the demo's gave us a good idea of how to connect up to Google Spreadsheet, Calendar etc. which was surprisingly easy. Also worth noting is that the client library is not just in Java but the community has it ported to Ruby, PHP, Lisp etc.
I called it a day after those sessions, will be heading out again tomorrow morning to catch the "Thinking in Flex" session and some other great presentations.