In general, after the 'easy' gains on a decently researched machine learning problem have been done, a new approach that gets, say, a 2% increase (say, from 91% to 93%) is considered a significant breakthrough and happens rarely - 5-10 years or so. 80%->85% is great. 80%->95% could be called work of the gods, given the 4x reduction in error rate.
