BlackBerry has thankfully maintained the really easy shortcut the PlayBook introduced for taking screenshots on BlackBerry 10. You simply hold down both the volume up and down buttons at the same time and you will hear a quick “snap” sound. The screenshots can then be found in the Camera folder on the phone (not the SD card).
I am hoping BlackBerry expands this feature a bit allowing you to quickly email off the screenshots you take or compress them. Better yet would be them opening it up as an API for developers.