I use both, often at the same time to do (almost) the same thing. Redundancy or just me being a complete nut?
For net based work, it has to be GUI, otherwise Susan would remove various parts of my anatomy while I sleep, and show the me pickled evidence the next day. Saying this, six months Susan would have killed me if I told her to "open a terminal and type in <whatever>". Now, she generally defaults to this approach when I'm about to explain something to her. Which is strange as I'm using Mandriva LE 2005 and everything she needs I've configured to be done via the GUI (even downloading the photos from my camera now works through FLPhoto... previously I had to manually download via CLI using gphoto2).
As a web developer I use a variety of tools, although I do default to CLI vim when I start building web structures, only after a basic shell of a page is built do I switch to Quanta+. Each interface has its advantages and disadvantages, so I have both open to use all plus points