And lest we forget, reliably identifying sarcasm on the internet is pretty hard even for humans who have all the requisite cultural knowledge. Unless the secret service can turn on the twitterer's webcam and observe their facial expression while they type, this really is a no go.
I think what will happen is for any given target a weighting will be inferred, giving the likelihood of that person being sarcastic or joking.
As more and more data about us is collected, about what we say/type vs. what we actually do, this has the potential to become more accurate over time.
Facial and voice-tone analysis, analysis of our peers' responses to what we say/write, analysis of our actual movements/purchases compared to what we say/write ("I'm so going along to that Nickelback concert at the weekend...!") etc., combined with leading brains in stats and ML lead me to think this problem could be tractable to some extent in the future. Scary :-/
If something like this comes to be, and is deployed 'wholesale', it has the potential to influence our behaviour, and over generations, alter our definition of 'sarcasm' by what we are able to get away with saying. Insidious!
That said I hope Charlie is right and that humans can game the system significantly that it is a non-starter.
I'm upvoting this because of the extent to which it illustrates my point. Or, conversely, the extent to which it plays along with my point. My head hurts.
Sarcasm doesn't work well on the Internet for the same reasons it doesn't work well in person when conversing with a stranger ... but the stranger has the advantage of reading your body language.
I was brought up in a family that used sarcasm heavily and "turning it down" on the Internet has been a real challenge. Sometimes I still fail (something I believe is obviously sarcastic is misread).
And we all know that could never happen.