JetTip succeeds because it focuses on user experience. Every aspect, including user registration and alert configuration, was designed with the user in mind.
JetTip's arrival / departure boards include several exclusive filters that make watching airplanes more enjoyable. Aircraft with unusual paint jobs "special liveries," or that are otherwise of interest to an aviation enthusiast, are shown by default. If an aircraft is unusual enough to trigger an alert, it gets highlighted.
Nick Benson, JetTip