Note that if you want to map a key to the escape character, you need to press ^v (control-v) first.
In eric+'s writeup (and most other vi oriented material)escape is written ^[. Just typing 'shift-6 [' won't work. The proper method is to press ^v, followed by the key labelled Esc.
Also, for mapping ^x, you can't use 'shift-6 x' either. Press 'control-x' or 'control-v control-x' instead.
As a result, ^v is a used key. ^z and ^c are used too (for suspending and interuppting vi on UNIX systems).
Of course, you could have figured this out by reading the documentation, but if you wanted to copy-paste the above, and are now baffled by the fact that it doesn't work - you know now.
I'm talking about nvi (a much used vi clone) here, by the way. There may be other implementations which act differently.