Approximately one month ago, I required some specific AJAX functionality.
Needless to say, my best friend Google came through as always.
I found jQuery PeriodicialUpdater. It worked as advertised, though it lacked a few features required for a production environment.
To make a long story short, in the end I coded the features myself.
The result can be found on GitHub.
GitHub repo: http://github.com/fwhite/JQuery-PeriodicalUpdater