jquery: how to remove blank fields from a form before submitting?

One way would be to set the “disabled” attribute on those fields, which prevents their values from being serialized and sent to the server:

$(function()
{
    $("form").submit(function()
    {
        $(this).children(':input[value=""]').attr("disabled", "disabled");

        return true; // ensure form still submits
    });
});

If you have client-side validation, you’ll also want to re-enable these fields in the event of a validation failure:

$(':input').removeAttr("disabled");

EDIT: repaired bug