I tried out the plsm2 using the CVS check-out. First, I had to make it actually build against the 1.4rc1 Ogre package (it was missing some references); second I had to fix the resource paths, and reverse-engineer where things were supposed to go (the install instructions aren't exactly crystal clear), and then after getting the map splitter to work, I still couldn't get it to load a terrain. At that point, I decided to go back to the regular terrain manager for now.
I did get a ways towards integrating Lua, though. I chose to adapt a very narrow layer on top (using C++ templates for variants and functions) I've written before -- re-use my own effort, rather than someone else's :-) The main problem with the libraries I looked at (toLua++, SWIG, and two others) were that they tried to solve to many problems, and thus become too heavy for just dropping scripting into an application. I don't want to subclass multiple-derived classes into Lua. Really!