I really enjoyed your plugin, I have written my own off of it that adds:
* http://codex.wordpress.org/Function_Reference/get_post_custom to return a meta index of all "Custom Fields"
* updated for php5+ adding hook in new __construct() with object ref
* allow for GET and POST methods
* added aditional hook for wp_ajax_nopriv_xxxxxx so users that aren't logged in can still query
I will re-release this as WP Ajax Query 2 if you are not maintaining it... otherwise I will give you the code and just add my name as a contributor ;) I'll give you a month or so to respond before I do, no rush. Shoot me an email at ringzer0 [AT] ymail [D0T] com