I am happy to announce that the paper 'Detecting treatment-subgroup interactions in clustered data with generalized linear mixed-effects model trees' is out as a working paper. So read all about it here. Or type install.packages("glmertree", repos="http://R-Forge.R-project.org") in your R prompt (not on CRAN yet, still very, very underground (read: pre-beta)).

The paper has been (is being) written together with Niels Smits, Achim Zeileis, Torsten Hothorn and Henk Kelderman.

And what do you get when you sloppily abbreviate generalized linear mixed-effects regression tree? You get a... a... a... GLIMMERTREE! And it isn't even Christmas yet.