http://www.equalizergraphics.com/
In my quest for better Blender viewport research I stumbled upon this. Might be worth looking further into. I couldn´t find a complete License yet but it is open source and the page says it´s LGPL along with: “Equalizer uses a liberal license which allows usage in both open source and commercial products. The license ensures progress on the core framework and protects the ISV’s investment in the future.”
I guess the majority got no idea now what a middleware for parallel OpenGL is or what it means, what this thread is about or why anyone should be excited 
Well:
If you´d squeeze it in Blender it would basically be an API between OpenGL and Blender. It would allow to parallelize OpenGL renderthreads across multiple GPUs in a system and even multiple GPUs in a network, work crossplatform and manufacturer independend.
For the gamers: something like OpenGL SLI+Crossfire.
So if you´d have a 100mio poly model, or a pointcloud and your viewport is too slow, you could just put a few more cards in your system, or hook up cards from network machines - where I already doubt that the performance over the network would be good for viewport, maybe for other tasks though.
It would also allow to split one OpenGL screen over several displays, where each display would be on one card, and each card would exclusively render only the part of the OpenGL screen that is on the cards display.
There´s also an Ogre3D integration.
It´s also integrated in FlowViz for GPU calculation of surface water flow models.
Bino Player a free Stereo3D player uses Equalizer to display over several displays, like Big Buck Bunny
Here are videos and images of the magic:
http://www.equalizergraphics.com/gallery.html
I am quite excited, I think this is a grand piece of software with many practical applications - almost too good to be true.
All we’d need now is a volunteer to quickly implement it in Blender…