Heh, that sidebar in the screenshots looks ridiculous. Basically seems like the opposite of vim…but yeah, NERDTree is pretty sweet.
leader-t to NERDTree’s toggle command and I generally hide it when I’m not using it. This has the added advantage that there is a single command to move focus directly to the tree and open a new file in my most recent split.
I also have the luxury of using pretty big screens most of the time…my regular work monitor can display three vertical splits side-by-side comfortably (110-char lines with a reasonable font size) if I leave NERDTree closed.