gistfile1.js

// ==UserScript==
// @include http://twitter.com/*
// ==/UserScript==

window.addEventListener('DOMNodeInserted', function (e) {
	var f = e.target.firstElementChild;
	if(f && f.className == 'main-content') { 
		addTweetEvent(f.querySelector('.twitter-anywhere-tweet-box-editor'), f.querySelector('.tweet-button'));
	} else if(e.target.className == 'twitter-anywhere-tweet-box-editor') {
		addTweetEvent(e.target, document.querySelector('.twttr-dialog-container').querySelector('.tweet-button'))
	}
	function addTweetEvent(textarea, tweet_button) {
		var textarea_focus = false;
		textarea.addEventListener('focus', function() { textarea_focus = true; }, false);
		textarea.addEventListener('blur', function() { textarea_focus = false; }, false);
		textarea.addEventListener('keyup', function(e) {
			if(e.keyCode == 13 && e.ctrlKey && textarea_focus) {
			e.preventDefault();
				tweet_button.click();
			}
		}, false);
	}
}, false);

gistfile2.js

// ==UserScript==
// @include http://twitter.com/*
// ==/UserScript==

window.addEventListener('keypress', function(e) {
	if(e.keyCode === 13 && e.ctrlKey && document.activeElement.className === 'twitter-anywhere-tweet-box-editor') {
		var button = document.activeElement.parentNode.parentNode.parentNode.querySelector('.tweet-button');
		button.click();
	}
}, true);