Since then, I have managed to get Naive Bayes running in NLTK and it performs particularly well, almost in-line with SVM and above Maximum Entropy. I have been able to combine the three classifiers in a max-votes strategy, with the results:
weighted precision 66.74% modified precision 78.12%weighted recall 67.29% modified recall 75.86%weighted fscore 67.01% modified fscore 76.97%
Its important to remember that these (finalish) results are based on single annotations.
As I'm currently getting more annotations, I will update these with hopefully better performance
(but on a smaller subset of articles).