I don't know - I live in the terminal, and I definitively wouldn't use it for regular commands (sed, grep, tar, etc), but if it was smart enough, I could see myself using it for software that I rarely use and which has complicated options.

For example, I'd rather type

  please convert movie.avi to h264 at 720p with subtitles from movie.srt 

than having to read the man page of avconv each time.

Bonus points if it could print the translated command before running it - it'd double as a learning tool.