They would never work together, but if they did we could probably have more technological advancements than we do now, but everyone needs a rival I guess.
I doubt they would, PS3 got shredded to bits by the 360, so i think sony might even go outta business or sell out or stop making games or something. or maybe microsoft will buy them out and just get rid of the company. but the idea is nice, id like to see that.