The vote has started for the 0.4 Mahout release. Lots of new stuff, but the part that I am excited about is a fairly comprehensive implementation of logistic regression suitable for large scale training and high speed classification, but there is a whole lot more.
With the 0.4 release, Mahout is moving along strongly towards the fabled 1.0 release. At that point, we will start paying lots of attention to backwards compatibility. That will be good, but the current wild and wooly policy is pretty handy if you have something in mind that Mahout really, really needs because we can get new things in pretty readily right now.
See http://mahout.apache.org/ for the release when it arrives and watch my twitter feed for an announcement.