Lion has a neat little feature discovered by @AppleFortyTwo. If you need a word looking up, three finger tap on your multitouch pad and hey presto, a neat dictionary pop up appears. See picture.
9To5 Mac are also reporting that the integration of Dictionary in Lion is much more prevalent including iBooks integration and an official SDK allowing developers to integrate Dictionary with ease. They also report seeing much more integration in iOS 5 for Apple mobile device suite.