Really? I'd think that most ML people are well aware of the importance of data cleansing and feature extraction. Also my experience is that domain knowledge oft

Really? I'd think that most ML people are well aware of the importance of data cleansing and feature extraction. Also my experience is that domain knowledge often (but not always - depends on the domain) helps surprisingly little. Feature extraction is mostly an iterative approach anyway: you define some very simple features, you look at the mistakes, you add some features and repeat until you are happy. Ideally you also do some visualization in there somewhere.