gnome-screenshot ('Screenshot' in the unity launcher) has three modes - full screen, current window, and selected area. But did you know that by default in Ubuntu 14+ there are keyboard shortcuts for not one, not two, but all three?
PrtSc for full desktop
Alt-PrtSc for current window
Shift-PrtSc for a selected area.
The first two will be familiar to Windows users, but the third keyboard shortcut is pretty cool too.
Except for the fact that you still have to use the mouse to select an area, so you can't go full keyboard ninja. Unless you have a cool keyboard based mouse movement system, then good for you!