Using Conditional Random Fields for Sentiment Extraction

I found this paper to be very helpful in understanding how to use Conditional Random Fields. Have a look. They are trying to extract the source of sentiment from sentences. Their approach also uses extraction patterns in addition to CRFs, but I'm not entirely convinced that the extraction patterns help all that much in increasing P&R. Especially helpful here is a good, detailed description of the features they use for the CRF. They used the Mallet toolkit for the CRFs, too.