Developing some proficiency with commands such as find, xargs, sed, grep, etc. is where you can really gain productivity. There are studies showing that the perception that the command line is more efficient than a GUI is false; the GUI is actually faster. This may be true for relatively simple operations such as moving, copying, or deleting files, but by involving find, xargs, and a few pipes you can quickly accomplish operations that would be either very tedious or flatly impossible in most GUI file "explorers".
I am a believer in the CL, but I want to point out what "faster" can mean in these GUI vs CLI debates: On one hand, GUIs are probably faster if one is discovering a command in an interactive environment, but command lines and key oriented interfaces are probably faster for pure execution once one knows what one is doing in the same interactive environment.
sed, awk, xargs, friends aren't used interactively like either of the above, but are rather super powerful ingredients of non-interactive environments.
Every study I've seen like this is indicating that they're faster to learn for the average joe, and possibly faster for certain types of tasks (stretching an image), not that they're faster in general -- I'm not even sure what exactly that would mean.
