I might have not been clear but DDs performance isn't generally bad, it only gets bad shortly before it crashes (which usually doesn't take long to happen).
I don't recall having trouble with other Unity games before but I just tried the Avert Fate demo and it was basically unplayable. Started off okay, but after about two minutes it was impossible to mouselook anywhere without the camera jerking a full 90-180 degrees in whatever direction it was turning. Not to mention very poor framerate on the default graphic setting. I shut it off before it could get worse.
So it probably is a Unity issue. Maybe. But it probably isn't a browser plugin issue (I use AdBlockPlus and NoScript, but the only things blocked on the DD launcher page are wordpress and twitter).
I have no firewalls or AVs running. Also, my active services are kept to a minimum: