A smarter `checked` and `value` binding that play nice together.

knockout.extendedCheckedBinding.js

// Now you can bind your checkbox selection to an observable array of model 
// properties, instead of having to bind it to a property on the item 
// itself (e.g. `isSelected`).

// For more information, see: 
// 	http://kamranicus.com/Blog/Posts/61/a-smarter-checked-binding-for-knockoutjs
// For a demo, see: 
// 	http://jsfiddle.net/kamranayub/G8YZU

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);
	}
};

var oldCheckedBinding = ko.bindingHandlers['checked'];
ko.bindingHandlers['checked'] = {
    'init': function (element, valueAccessor, allBindingsAccessor) {
        var allBindingsValue = allBindingsAccessor(),
            modelValue = valueAccessor(), unwrappedValue = ko.utils.unwrapObservable(modelValue);
        
        if (allBindingsValue.hasOwnProperty("value") && (element.type == "checkbox") && (unwrappedValue instanceof Array)) {
            var updateHandler = function () {               
                // 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 = ko.utils.unwrapObservable(allBindingsValue.value);

                // Update values
                modelValue = valueAccessor();
                unwrappedValue = ko.utils.unwrapObservable(modelValue);
                
                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);                
            };
            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 });
        } else {
            oldCheckedBinding['init'].apply(this, arguments);
        }       
    },
    'update': function (element, valueAccessor, allBindingsAccessor) {
        var value = ko.utils.unwrapObservable(valueAccessor()),
        	allBindingsValue = allBindingsAccessor();

        if (allBindingsValue.hasOwnProperty("value") && element.type == "checkbox" && value instanceof Array) {
            var boundValue =  ko.utils.unwrapObservable(allBindingsValue.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 {
            oldCheckedBinding['update'].apply(this, arguments);
        }
    }
};