I used Vis full time for a two weeks a couple of months ago. It was pretty nifty. (I'm Emacs user so this was an time-bounded experiment).

Vis is a great of example of the suckless philosophy and of Guy Steele's point about removing the need of features by having synergy between other features. For example they have an immutable piece table to support undo by just moving a pointer. This would mean that as the buffer remains open one would use more and more memory. Instead of implementation a 'garbarge collector' they chose to automatically close a file when its not shown on the screen.