Hey HN: Thoughts on the validity of the new app ToneCheck?

We all know how big contextual advertising is... driven largely by the success of the Google AdSense platform. I just caught wind of a new application called ToneCheck (http://www.tonecheck.com) which claims to be able to estimate the overall tone of a sentence in your emails prior to sending them out. Thoughts on whether this has successfully been done before? There's plenty of sharks out there in the marketing world who have been trying to perfect this for years. I mean, what better way to target and analyze your users than by dissecting their emails and being able to check for tone and sarcasm to reduce false positives/negatives.