Mahout currently has
Collaborative Filtering
User and Item based recommenders
K-Means, Fuzzy K-Means clustering
Mean Shift clustering
Dirichlet process clustering
Latent Dirichlet Allocation
Singular value decomposition
Parallel Frequent Pattern mining
Complementary Naive Bayes classifier
Random forest decision tree based classifier
High performance java collections (previously colt collections)
A vibrant community
and many more cool stuff to come by this summer thanks to Google summer of code
I'm interested in machine learning techniques (graphical models, kernel methods) applied to text understanding (entity and relation extraction, coreference resolution, document classification and clustering, confidence prediction, social network analysis, data mining).
P. Cimiano, and J. Völker. Proceedings of the 10th International Conference on Applications of Natural Language to Information Systems (NLDB), volume 3513 of Lecture Notes in Computer Science, page 227-238. Alicante, Spain, Springer, (June 2005)
J. Tang, H. fung Leung, Q. Luo, D. Chen, and J. Gong. IJCAI'09: Proceedings of the 21st international jont conference on Artifical intelligence, page 2089--2094. San Francisco, CA, USA, Morgan Kaufmann Publishers Inc., (2009)
C. Brewster, F. Ciravegna, and Y. Wilks. NLDB '02: Proceedings of the 6th International Conference on Applications of Natural Language to Information Systems-Revised Papers, page 203--207. London, UK, Springer-Verlag, (2002)