One of the features I miss the most from Emacs when using Vim is the ability to mask certain strings as other strings (eg. Unicode symbols). The most often used case for this is when dealing with Greek characters (such as lambda), or when writing Tex.

Luckily, a guy named Vince Negri wrote a patch for Vim to provide a "Conceal" functionality. Most of the examples I've found for using this functionality deal with either Tex, or only with certain languages. It turns out it's pretty easy to force it for all file types though, simply place this at the end of your .vimrc:

au VimEnter * syntax keyword Statement lambda conceal cchar=λ
au VimEnter * hi! link Conceal Statement
au VimEnter * set conceallevel=2

And enjoy your beautiful new λ's :)