Well, in one of my games I freed a Dyson Sphere, and he kinldy do not shoot me and can even be considred an ally.
And even better then that, he saved one of my most importent border worlds during a Cross Planet Attack.
My planet was invaded by 1000 space plane IIs, but dyson had 67 dyson gatlings battling them thus saving my command station, the counterspy unit and the second WH defence.
The planes eventually just cloaked up somewhere (can't leave since I got a Black Hole Machine built there) and my counter spy is finishing them off.
Nothing soecial I guess, but I really did like this turn of events, as my main fleet was away on the otherside of the galaxy, and I could otherwise have lost a lot of importent systems if not for the dyson since the AI really did steamroll my WH defence.
Anoy other expereinces with dyson?