Capturing screenshots on Samsung Galaxy S and Other Samsung Android is very easy post Froyo update on them. No need to use infamous stock android screenshot facility where we use SDK method by enabling USB debugging etc.,
Its just two step process now to take a screenshot.
1. Hold the back key
2. Click the home key by holding the back key, your phone will vibrate and you'll see a message on screen saying “Screen captured, saved as image file”. Go to Gallery and you'll see a folder called 'ScreenCapture' where you can find your screenshots.
This feature is probably available on other Samsung Android devices too like Galaxy Tab.
Note: Screen capture may not work for some apps where it exits immediately the moment you hit back button.