I like to use use Gingko while I'm hard technical material. I basically just re-write a much more condensed version of the textbook as I read through it.

Here's my Gingko map of Sivia's Data Analysis: A Bayesian Tutorial.

EDIT: fixed the link

Also, I should note that I think a lot of the benefit of using Gingko is the simple act of putting the notes into it (because it changes the reading experience from passive to active).

I'm not so sure it's that reading the Gingko tree is useful.