Q:

Submit fires even if email.value == ""

I'm making a simple form where a user submits a video, alongside their email address. I'd like to make it so that the person can not submit the form until they have filled in the email and saved the video.
The video part is working, but when I test with an empty email, it still seems to submit. The code is below, and the live version is at http://www.atlas-china.com/record-your-multi-lingual-abilties/
Help much appreciated! 
// Global variable to hold player's reference.
var _Nimbb;

// Global variable to hold the guid of the recorded video.
var _Guid = "";

// Event: Nimbb Player has been initialized and is ready.
function Nimbb_initCompleted(idPlayer) {
    // Get a reference to the player since it was successfully created.
    _Nimbb = document[idPlayer];
}

// Event: the video was saved.
function Nimbb_videoSaved(idPlayer) {
    _Guid = _Nimbb.getGuid();
}

jQuery(document).ready(function ($) {

    // Get the data from the form.  Check that everything is completed.
    $('#video_submit').click(function (e) {

        var email = document.getElementById("email").value;
        var video_title = document.getElementById("video_title").value;
        var form = document.myForm;

        // Make sure the email is specified.
        if (email.value == "") {
            alert("Please enter your email to proceed.");
            return;
        }

        // Verify that the video is not currently recording.
        if (_Nimbb.getState() == "recording") {
            alert("The video is being recorded. Please wait.");
            return;
        }

        // Check that video has been recorded.
        if (_Guid == "") {
            alert("You did not save the video.  Click save.");
            return;
        }

        // Set the guid as hidden parameter.
        form.guid.value = _Guid;

        var dataString = 'email=' + email + '&guid=' + _Guid + '&video_title=' + video_title;
        //alert (dataString);return false;  
        $.ajax({
            type: "POST",
            url: "<?php echo get_template_directory_uri();?>/send.php",
            data: dataString,
            success: function () {
                $('#contact_form').html("<div id='message'></div>");
                $('#message').html("<h2>Contact Form Submitted!</h2>")
                    .append("<p>We will be in touch soon.</p>")
                    .hide()
            }
        });
        document.forms["myForm"].submit();
    });
});

A:

After viewing your live site...
email = "" // Empty string

Whereas 
email.value = undefined 

Try changing your code to 
if (email === "") {
    alert("Please enter your email to proceed.");
    return;
}

I assume you are doing .value twice by mistake as you have the following line earlier in your code
var email = document.getElementById("email").value;

