I've been using an external trackpad instead of a mouse since around 2009. At first, I used ratpoison as my window manager on my EEE PC as a daily driver, which is controlled entirely via the keyboard, then I used StumpWM for a long time and now I use cagebreak (which is a Wayland compositor with ratpoison-like behaviour). I use the trackpad very sparingly, only when it’s really necessary.