I can't imagine myself using a GUI for git, but there are some things that are faster with a GUI and mouse than with a keyboard. Almost all of them involve some kind of visual feedback. For instance, lately I've been working on some projects that involve absolutely positioning HTML elements on the page. This is a huge pain using a text editor--you make an estimate, save it, reload the page, see how it looks, and repeat. Just clicking and dragging is much, much easier.
Other than that, I generally think that keyboard is a faster input, though an 80-character terminal window is often a poor choice for visual feedback. Termkit has some interesting ideas: http://acko.net/blog/on-termkit/
For the future, mnutt: I love Chrome's developer tools, you can directly edit CSS rules from the browser by right clicking on it and selecting inspect element. Helps a lot with these situations!
Other than that, I generally think that keyboard is a faster input, though an 80-character terminal window is often a poor choice for visual feedback. Termkit has some interesting ideas: http://acko.net/blog/on-termkit/