Since I temporarily have HN's attention with this side blog of mine, can I suggest one simple tweak:

Please, please, if your site requires AJAX to work at all, then retry failed AJAX queries. Use exponential backoff or whatever but don't let the AJAX query fail once and the page be unusable.

This happens all the freaking time when I'm on dialup, and there's nothing more annoying than having filled out a form or series of forms only to have the submit button break because it used AJAX to do a sanity check and threw an exception because the server timed out after some absurdly short (dialup-wise) period of time.

-- Joey Hess