Happy new year! It's been a nice holiday break, but it's good to get back to work. First, some catching up.
The IR Group at Glasgow released Terrier 2.2 right before Christmas, see their blog post for details. It's a major update because it adds support for distributed map-reduce index creation using Hadoop. There is currently no equivalent for distributed retrieval, but they are working on it.
I haven't seen formal performance numbers, but from what I hear it is quite scalable; it should be able to index billions of documents on a commodity cluster.