Would a KVM solution like Synergy address your needs? eg an iMac and MBP side by side sharing a keyboard and mouse?
What's not optimal is the price of these things, however. I liked the fact that I could hook standard displays up to my Mac Pro, but the multi-Thunderbolt solution looks workable as long as one is willing to shell out a thousand USD/EUR per display.
I had tried synergy a few times and never succeeded.