Interesting site...and could be useful if your meeting someone at the airport. Flightradar24.com - Live flight tracker!
I have the paid for app, I used to tell you certain emergencies, also good if you want to see what aircraft you'll be flying to your holidays.
Do not go near this app guys, it has addictive tendencies, it slowly turns you into a plane spotter.......then you start looking at vessselfinder....its a dangerous downward slope you are starting out on