My sister and I lucid dream every so often, though she also actively experimented with inducing them when we were younger (using the reality checks mentioned above), and managed to get near-full control once or twice.
Usually all I can do is predict or slightly sway the course of a dream; I've never gotten full control, since I generally can't violate any ground rules the dream has without starting to wake up. By the same token, though, I can take advantage of any fun laws. So, for example, if the dream "allows" flying, I can do so -- but if there are conditions, like I have to take a running start, or it has to be done in a certain area, then I can't just take off standing from anywhere.
I've found good lucid dreams can be incredibly restful and relaxing, but bad ones can be headache-inducing, especially if I've been trying to wake up from them. And there've been a couple unsettling ones where I only realize upon waking up just how much I had let my id run amok despite (or because of) the added self-awareness.
In conclusion, is Osaka a butterfly dreaming it is a Japanese high school girl? Or is she merely with a Chiyo-chichi dreaming that he is a bird?