Re: Stopping the browser throbber
I'm the one building the backend. It would certainly work with javascript/DOM (and the multiple frame idea). In fact, we're looking into that, as we may have multiple "applications" on the same web page that need to be updated, and don't want each one to have its own connection.
The page will continue to eat memory if you use this method. We opted against it.
You can service a number of frames/applications with one applet fairly easily. Basically, you put some javascript in the top frame that 'reads' the page looking for tags with particular realtime indicator attributes. The javascript is kicked off by the applet. The applet uses the information to build a list of events to subscribe to, and sends that back to the server as a startup.
As far as the requirement... all of our application is web-based. Realtime is merely an outgrowth of the need for up-to-date data.
WRT to sizing: we haven't sized it fully yet. Currently only a small portion of the app is realtime enabled.