&quot;Support Vector Machines (which as I understand it are largely dead, but the theory behind them is interesting and could lead to more developments).&quot;<p>Wow, that happened fast.  SVMs seemed all the rage a few years ago.<p>I think it shows the importance of understanding the formalisms underlying machine learning approaches, and their corresponding strengths and weaknesses.  Neural networks had been on the outs for a long time, before the realization that having much more data to train against could massively increase their usefulness.<p>Wonder what the next ML technique to see a resurgence will be.