How is the undo tree used in Vim?

Question

This answer says:

Vim\'s undo/redo system is unbeatable. Type something, undo, type something else, and you can still get back the first thing you typed

Answer 1

I'm a bit late to the party, but I figured I'd mention that I wrote an undo tree visualization plugin for Vim: http://bitbucket.org/sjl/gundo.vim/

Personally I found that graphing the tree like this was the only way I could make sense of it.