I've noticed mentions of 0w30 oil helping MPG. Does this apply to any car, or only to an Insight? The same with tire pressure?

I am still shopping for a hybrid, and trying to decide between the models. I drove a Prius, but it was a beat up demo that made funny grinding noises that the saleman was clueless about. I haven't been able to find an Insight to drive in SE Michigan.
I love the feel of the Accord hybrid, but I am drawn to the incredible MPG reported by Insight drivers.

p