This raises some flags for me:

* Writing from insert mode seems like a gross way to cross the modal editor boundaries to me. You could save keystrokes by mapping lots of meta keys in insert mode, but then you'd be using Emacs. I also think you end up losing keystrokes, because you no longer have clearly defined actions that can be repeated using `.` or macros.
* Why is writing such a common action? Don't you always write and then do something else? Using `autowrite` or adding a `:w` do common commands seems like a better way to handle this by removing the superfluous write action. If you find yourself just writing a file without doing anything with it, I'd be interested to know why.