Some go below it, some have thrice that.
If you are an avid FPS gamer, you should definitely look for a monitor with 10ms or less input lag.
Note: response time does not describe input lag. Two completely different things. You're better off just ignoring response times completely.
Input lag is not an advertised spec. You usually find it in monitor reviews. There they hook it up side by side with a CRT (because CRTs have no input lag) and display a counter on the screens, and take pictures of the monitors with a a high shutter speed setting on a camera. Dozens of pictures. Then they compare them and calculate an average input lag for the LCD monitor.
Input lag is an issue on a plenty of monitors. Most TN panels don't have it bad though.