Also, using glCopyYadder to capture the scene depth buffer was being limited by the app window size, so I've been forced to make the jump to using frame buffer objects too - delving into a rather arcane and temperamental part of OpenGL (boy is DirectX looking (slightly) more attractive nowadays, especially with the Longs Peak debacle. /me remembers back to my first blog comment...)
Getting the shadows integrated (I have to sample the shadow texture in each shader) also revealed errors in the ambient lighting calculations in the terrain and mesh shaders, which was nice.
Anyway, nuff yacking, here's how shadows change the look of the old gfx... (yep: could do with some textures about now I think). I'm now looking at overcoming the various idiosynchrasies as we speak. Ysaneya's journal has been quite helpful here describing his journey through the same territory.