In the US at least, the FAA's official data feed (ASDI) is delayed by at least 5 minutes. The undelayed data is only given out on an as-needed basis (e.g. to airline operators) and can't be redistributed to the general public.
In Switzerland, the federal aviation authorities tried to impose a delay as well. After a wave of protest pointing out the absurdity of such security through obscurity – you can see aircraft in the sky after all! -, a delay is no longer necessary and you can check in real time which aircraft is flying over your head at the moment (if equipped with ADS-B).