Storing a DateTime Value in a Sortable Custom Field?

Yes, you can use jQuery DatePicker and save the date, and use query_post to show the postS in order (code also on github):

<?php
//The Query
// exactly than
query_posts('meta_key=start_date&meta_value=".date("Y-m-d"));
// or
// dates less than
// query_posts("meta_key=start_date&meta_compare=<=&meta_value=".date("Y-m-d"));
// or
// date mayor than
// query_posts("meta_key=start_date&meta_compare=>=&meta_value=".date("Y-m-d"));

//The Loop
if ( have_posts() ) : while ( have_posts() ) : the_post();
 echo the_title();
 echo "<br />";
endwhile; else:
endif;

//Reset Query
wp_reset_query();
?>