Sentiment analysis of digitized content (tweets, email, blog posts, etc) is hard. Sarcasm makes it even harder. Consider how many sarcastic comments are made in our online communications each day. "I love being delayed at the airport." "I can't stand it when everything is going my way." etc. Analyzing text like that has got to throw even the best sentiment analysis engines for a loop, and the false positives start flying.
If you're sarcastic, like me, you've learned to keep your sarcasm to a minimum when you're writing because the context just isn't there for your reader, much less a machine, to understand the subtle shifts in tone or where you're coming from.
I'm looking forward to sentiment deduction getting better, but I'd like to see how the logic evolves to understand age-old sarcasm.
Maybe we will all just stop being sarcastic to support the machines running our lives.