Consider detailing how this position can help in candidate's development. What he/she could learn, what interesting[#] tools will be in use, things like that.

I hear way too little about that from recruiters, and even then, only clichés like "international team" or "bleeding-edge technologies".

[#] Django, Ruby and MongoDB are not considered interesting here. There's plenty of places where one could use them. On the other hand, opportunity to use Coq, for example, would be very interesting.