Allows you to use "1", "2", "3" and "4" to press the review buttons in the review tools.

ReviewKeyboard.user.js

// ==UserScript==
// @author Tom Wijsman
// @name Review Keyboard
// @description Allows you to use "1", "2", "3" and "4" to press the review buttons in the review tools.
// @include http://*superuser.com/review-beta/*
// ==/UserScript==

function EmbedCodeOnPage(javascript_code) {
        var code_element = document.createElement('script');
        code_element.type = 'text/javascript';
        code_element.textContent = javascript_code;
        document.getElementsByTagName('head')[0].appendChild(code_element);
}

function EmbedFunctionOnPageAndExecute(function_contents) {
        EmbedCodeOnPage("(" + function_contents.toString() + ")()");
}

EmbedFunctionOnPageAndExecute(function() {
	function keyCheck(e)
	{
		if (e.keyCode >= 49 && e.keyCode <= 52 && $('.comment-form textarea').length === 0)
		{
			var reviewButton = $('.review-actions').find('input')[e.keyCode - 49];
			if (document.createEvent) {
			        var event = document.createEvent("MouseEvents");
			        event.initMouseEvent("click", true, true, window,
		                	0, 0, 0, 0, 0,
	                		false, false, false, false,
			                0, null);
			        reviewButton.dispatchEvent(event);
			}
			else if (reviewButton.fireEvent) {
			        reviewButton.fireEvent("onclick");
			}
			else {
				window.alert('Your browser is not supported.');
			}
		}
	}

	window.addEventListener('keydown', keyCheck, true);
});

Good idea!