What jimlintott said goes for me:
Well, both, kid of -- I love my GUI (KDE is my choice for desktop) but I mainly love it because I can launch a bunch of terminal windows. My most-used applications are probably (in roughyl order from most-used to least): bash, vim, and perl -- with nods to grep and locate.
In fact the only GUI based application I use on a regular basis is -- besides the terminal emulator -- Firefox (and Konqueror -- it rocks!). But I also lean heavily on wget, curl, links, lynx, and even netcat. There's a bag of tools right there.
I find the difference between the GUI and the commandline boils down to one of "discovery." If you don't know quite what you want to do, the GUI is a great way to figure it out. If, on the other hand, you know exactly what you want to do, the commandline is typically the best way to do it. It's a bit harder to learn and you're tasked with either remembering the options you use or looking them up constantly... but if you can manage all that, then the power of pipes is absolutely freaking unstoppable.
Speaking of which, I've heard a lot about the new pipe-like system in .NET. MS is finally trying to catch up to that kind of power. Unfortuantely, they seemed to miss the boat a bit, we'll see how it works out.