Type this in the terminal:
import -window root screen.png
If you just do "import screen.png", you'll get a little cross to select the area that you want.
You can put this in a launcher, or even better, go to Keyboard Settings and assign the Print Screen key as a shortcut to the command.
EDIT: I didn't realise that the thread you mention already contains this command as a solution. Well, if you put in in a launcher in the panel, desktop, or menu, it does the job very well. But if you would like something a bit more fancy and with a graphical interface, there's nothing in the repos so far as I can see.