I found more or less by mistake how to make a screen capture on the Galaxy S Android mobile. Other such instructiond requires the installation of an SDK or similar but this anyone can do really.
Go to the screen you wish to capture. Then press and hold the back/return button for a couple of seconds and then hit the middle button. A camera shutter sound is played and the image is captured.
The picture can then be found int he gallery of the phone as would any normal camera picture be, it can thus be uploaded, shared with face book, blogged (actually I wrote this on the phone using a WordPress agent straight from the phone)
From Jonas comment below I would conclude this is a Galaxy S specific feature that is not android 2.2 common unfortunately.
All of us who like the Android and writes about specific software on the android would love to have this feature implemented so I will suggest it to Google and see what happens in the coming versions on Android.