my favorite example is "just read the book". it contains no explicit sentiment word and it is highly depending on the context. If it apears in a movie review it means that the-movie-sucks-it's-a-waste-of-your-time-but-the-book-is-good. However, if it is in a book review it delivers a positive sentiment.
And what about - "this is the smallest [mobile] phone in the market". back in the '90, it was a great praise. Today it may indicate that it is a way too small.
I think this is the place to start in order to get the complexity of sentiment analysis: http://www.cs.cornell.edu/home/llee/opinion-mining-sentiment-analysis-survey.html (by Lillian Lee of Cornell).
