NB: this is a preliminary version of my survey, I will complete it by April 10.

XHR: on success, on failure, pause an xhr and come back to it later.
XHR is built-in/taken care of, you can also write components that send XHR
"High-performance AJAX components should be developed using custom HTML-and-JavaScript-rendering synchronization peers that make asynchronous calls to their own server-side services."

Timer/Timeout.
timer: yes (UI is locked during client/server interaction however)
timeout: yes, using java.util.Timer

History/state (back button)
no

Off-line Storage?
may be able to save files to disk, but needs server to generate interface

Interaction with the Desktop applications?
no

Extensibility.
yes, you can write custom components and integrate it with other java programs

Animation.
yes (uses the scriptaculous animations)

Number of Items that can be displayed in the interface without causing memory or computation problems.

Amenable to other technology mashups/ javascript frameworks: Can it be used with other javascript frameworks.
with some work, yes (http://forum.nextapp.com/forum/index.php?showtopic=3406&hl=eval)

Support for stateless messaging? -scalability
yes, using TaskQueue

Usability? Bookmarking/Layout font-size changes
yes to font-size changes, no to bookmarking (url doesn't change)

Browser Portability
yes

Start Time? How big are the javascripts/swf files....
start time should be faster since entire app doesn't need to be downloaded initially

TESTING and Debugging tools. How can you test the GUI interface?
debugging possible in eclipse (since it's java based), also there's a JS debugging tool for viewing AJAX messages and the DOM

Will the generated HTML be portable and what happens when a new browser comes in?
not necessarily portable since the source is a JS file which renders all the HTML, however you can see the DOM through the JS debugging tool

Server/Client
server

Remote Process Calls? Different from JSON and XML
RPCs are hidden, developer sets event listeners

Batch XML Http Requests?
looks like you can create a queue of multiple requests