PG has a couple essays directly related to this topic. The first about using a language which is implicitly more powerful than others ("Beating the Averages") [1] and the other is about how using a less common language is a positive selector in the hiring process ("The Python Paradox") [2].
[1]: http://www.paulgraham.com/avg.html
[2]: http://www.paulgraham.com/pypar.html