Algorithm to determine how positive or negative a statement/text is

Question

I need an algorithm to determine if a sentence, paragraph or article is negative or positive in tone... or better yet, how negative or positive.

For instance:

<

Answer 1

Ah, I remember one java library for this called LingPipe (commercial license) that we evaluated. It would work fine for the example corpus that is available at the site, but for real data it sucks pretty bad.