Nice article on Angular deferreds, promises and things you may do wrong.

• use $q.when(['detail', 'simple']) for simple defereds
• use promise chaining whenever possible, like return $http....
• $timeout already returns a promise, so return $timeout
• use custom made deferreds when wrapping traditional callback APIs (like many of jQuerys)
• use return $q(function(resolve, reject){ ... }) directly (Angular 1.3+ only)