Java is very common these days but I still think you should consider making checking if browser can't support and put something on the display. Latest news or something.
Progressive jpgs I've never used but isn't it simply when you pack them choose progressive encoding etc.? If browser can't support progressive ones its their fault
BTW java applet appeared ok and for quick watch seemed to be working correctly. Applet is usually better than some horrible mixed sevrlet or so, applets look always the same 99% sure. Sevrlets might do something weird with different browsers.
