I'm not aware of anyone who uses mlpy, but I would be curious to hear about experiences with it.<p>In Python, for general Machine Learning I really like scikits.learn (<a href="http://scikit-learn.sourceforge.net/" rel="nofollow">http://scikit-learn.sourceforge.net/</a>). The library is Pythonic and includes many common ML tools I need.<p>I have heard good things about Shogun (<a href="http://www.shogun-toolbox.org/" rel="nofollow">http://www.shogun-toolbox.org/</a>), which is written in C++ and has bindings for many other languages, including Python. Shogun appears to be more focused on kernel algorithms (e.g. SVMs).<p>There's a GSOC project to bind Vowpal Wabbit in Shogun. That would be sweet. This was mentioned by John Langford on the VW mailing list.<p>Theano (<a href="http://deeplearning.net/software/theano/" rel="nofollow">http://deeplearning.net/software/theano/</a>) is great if you are devising your own ML models, particularly ones that are based upon gradient descent. It's Python and it automatically compiles to C/C++ and then machine code for your CPU or GPU.