I never got used to that, it seemed totally backwards to me. I can deal with it on a screen where my finger is (almost) physically attached to what I'm scrolling, but not on a detached mouse/trackpad and display.
I actually got used to it fairly quickly. After a day or two I instinctively used reverse (or "natural") scrolling, and I can switch back pretty easily when I'm using other people's computers. It does seem like almost no one else switched though.
I didn't just get used to the inverted scrolling, I fell in love with it. I think it makes perfect sense, and fells more "connected" with what I'm doing.