By default printscreen or alt print screen will get the whole desktop or the application in focus, respectively. But what if you want to select a portion of the screen?
gnome-screenshot:
ksnapshot
compiz
This is a nicely integrated solution
sudo apt-get install compizconfig-s........
This is what I call a ridiculous bug in compiz that causes it.
The solution/To fix it just install "compizconfig-settings-manager"
Open it up and Navigate to General Options -> Display Settings
Set the "Refresh Rate" to the current refresh rate of your monitor.
For ATI cards with slow window dragging/response supposedly disabling "Sync to VBlank" fixes that but otherwise leave it as is.........