[emillon]

Autocompletion does not have to be context-aware to be useful. "Dumb" completion of words in the current buffer, or filename, is quite useful IMHO.

[aerique]

Dumb autocompletion easily covers 50% of my cases and with Emacs hippie-expand (or one of its modern siblings) up to 75%: http://emacswiki.org/emacs/HippieExpand

That said, Emacs and Vim also have intelligent autocompletion depending on the language and support for it has only been getting better.

disclaimer: numbers have been made up