Impressive that it doesn't just take the best guess; it also informs you of its alternative hypotheses: http://i.imgur.com/wITwa.png Update: Reading your blog post, I see that this is a wrapper around highlight.js, which is doing the language-guessing (including the second-best guess): http://softwaremaniacs.org/wiki/doku.php/highlight.js:api
In conclusion, the site is a very good idea, but highlight.js is really too bad for this kind of use. Raise a ticket on highlight.js