A smarter `checked` binding and `value` binding, so you can bind the checked property of a checkbox to an array of model property values, rather than a string array.

knockout.extendedCheckedBinding.js

var oldValueBinding = ko.bindingHandlers['value'];
ko.bindingHandlers['value'] = {
  'init': function (element, valueAccessor, allBindingsAccessor) {

		// If `checked` binding is present, ignore this binding because
		// user wishes to bind the checked value to the model value
		var allBindings = allBindingsAccessor(),
			hasChecked  = allBindings.hasOwnProperty("checked");

		if (hasChecked) {
			return;
		}

		oldValueBinding['init'].apply(this, arguments);
	},
	'update': function (element, valueAccessor, allBindingsAccessor) {
		// If `checked` binding is present, ignore this binding because
		// user wishes to bind the checked value to the model value
		var allBindings = allBindingsAccessor(),
			hasChecked  = allBindings.hasOwnProperty("checked");

		if (hasChecked) {
			return;
		}

		oldValueBinding['update'].apply(this, arguments);
	}
};

ko.bindingHandlers['checked'] = {
    'init': function (element, valueAccessor, allBindingsAccessor) {
        var updateHandler = function() {
            var valueToWrite;
            if (element.type == "checkbox") {
                valueToWrite = element.checked;
            } else if ((element.type == "radio") && (element.checked)) {
                valueToWrite = element.value;
            } else {
                return; // "checked" binding only responds to checkboxes and selected radio buttons
            }

            var modelValue = valueAccessor(), unwrappedValue = ko.utils.unwrapObservable(modelValue),
                allBindingsValue = allBindingsAccessor();
            if ((element.type == "checkbox") && (unwrappedValue instanceof Array)) {
                // For checkboxes bound to an array, we add/remove the checkbox value to that array
                // This works for both observable and non-observable arrays
                var boundValue = (allBindingsValue.hasOwnProperty("value") && ko.utils.unwrapObservable(allBindingsValue.value)) || element.value;

                var existingEntryIndex = ko.utils.arrayIndexOf(unwrappedValue, boundValue);
                if (element.checked && (existingEntryIndex < 0))
                    modelValue.push(boundValue);
                else if ((!element.checked) && (existingEntryIndex >= 0))
                    modelValue.splice(existingEntryIndex, 1);
            } else {
                ko.expressionRewriting.writeValueToProperty(modelValue, allBindingsAccessor, 'checked', valueToWrite, true);
            }
        };
        ko.utils.registerEventHandler(element, "click", updateHandler);

        // IE 6 won't allow radio buttons to be selected unless they have a name
        if ((element.type == "radio") && !element.name)
            ko.bindingHandlers['uniqueName']['init'](element, function() { return true });
    },
    'update': function (element, valueAccessor, allBindingsAccessor) {
        var value = ko.utils.unwrapObservable(valueAccessor()),
        	allBindingsValue = allBindingsAccessor();

        if (element.type == "checkbox") {
            if (value instanceof Array) {
            	var boundValue = (allBindingsValue.hasOwnProperty("value") && ko.utils.unwrapObservable(allBindingsValue.value)) || element.value;

                // When bound to an array, the checkbox being checked represents its value being present in that array
                element.checked = ko.utils.arrayIndexOf(value, boundValue) >= 0;
            } else {
                // When bound to anything other value (not an array), the checkbox being checked represents the value being trueish
                element.checked = value;
            }
        } else if (element.type == "radio") {
            element.checked = (element.value == value);
        }
    }
};