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).
G. Solskinnsbakk, and J. Gulla. On the Move to Meaningful Internet Systems, OTM 2010, volume 6427 of Lecture Notes in Computer Science, Springer, Berlin / Heidelberg, (2010)
A. Plangprasopchok, K. Lerman, and L. Getoor. Proceedings of the 4th ACM Web Search and Data Mining Conference, (2010)cite arxiv:1011.3557Comment: In Proceedings of the 4th ACM Web Search and Data Mining Conference (WSDM).
R. Kohavi. Proceedings of the Fourteenth International Joint Conference on Artificial Intelligence, page 1137-1145. San Mateo, CA: Morgan Kaufmann, (1995)
D. Nguyen, N. Smith, and C. Rosé. Proceedings of the 5th ACL-HLT Workshop on Language Technology for Cultural Heritage, Social Sciences, and Humanities, page 115--123. Stroudsburg, PA, USA, Association for Computational Linguistics, (2011)