*hmm you know. I look on using multiple renderers as using different materials. each renderer has it's own unique output.. so it's like using Oils, Watercolours, etc.. depends on what I want for the render at the time.. *

(I personally use Lightworks (in truespace), Firefly (Poser), Kerkythea (Sketchup/any imported OBJ), Luxrender (Poser), and I hope Cycles if I ever get blender to behave)