Google Drives Towards Microsoft and Adobe With Gears
techcrunch.com
techcrunch.com
http://code.google.com/support/bin/answer.py?answer=83194...
(note that the nspluginwrapper link on their site doesn't work for Gears - it was reported by a poster on a mailing list as working, but future posts confirmed it doesn't do the trick)
...whereas both Flash and Moonlight work quite well on x64 now (nevermind the past).
But in terms of Javascript/HTML/AJAX, it compiles separate versions for each browser (which are automatically loaded), virtually eliminating the need to handle various quirky browser behaviors. And any standard Java app server works fine for the server side, nothing special needed there.