one thing I struggle with emacs is that I can't find a place which documents the emacs way of doing things. Emacs has multitude of features, there are just too many to master, yet even to know that they exist.

One example would be rectangle select http://www.gnu.org/software/emacs/manual/html_node/emacs/Rec..., I absolutely love them - but till one of colleague introduced them to me, I had no idea they existed.