vi intro -- the cheat sheet method
IBM has a good tutorial on vi (originally posted several years ago). Viewing the tutorial requires registration, but is worth it in my opinion.
Now, I have no intention of entering into the religious holy wars of emacs versus vi(m). I prefer the simpler path of enlightenment, myself, and tend to prefer the much more user-friendly newbie-oriented text editors like pico, nano, and gedit (kate's good too). Personally, I have always thought that one should be able to type something and actually have it appear on the screen at the same time, not have to enter a command mode and ask your editor permission first before actually being able to accomplish anything. But then again, I fell off the wagon of glory somewhere along the path of enlightenment long ago, so I have learned that expecting something intuitive often short-circuits enlightenment.
Seriously, I think it is good to know vi(m), even if I know I'll never use it until one of those dreaded "what if?" doomsday scenarios happens.