To know the Current Status of any website or web service just visit :
It also ensures you if there is any problem in any website . For example , If facebook is opening very slowly or taking a lot of time to login then just visit this website to know the status of facebook . At Present I can see there is a Service Trouble in Twitter 5 mins. back.
Up means there is no Problem in the website its running fine
Down means the website server is currently down so it will take time to access.