To remember for later...

macosxhints - Change the default location for screenshots:

To change the default location for screen captures so they get saved in a specific location instead of cluttering the desktop, you need to use the defaults command in the Terminal to change the path. It can be done like this:

Create the folder in which you want the screen captures to be saved in the location of your choice.
Open a Terminal window and type this:

defaults write location /Full/Path/To/Folder

Log out and log back in, and the change will have taken effect.