The reversing of the scrolling direction is certainly going to take a lot of getting used to. The new way feels semi-natural with the track pad, but with a mouse wheel not so much.
An hour or so was enough for me. Just one thing to unserdtand: you are moving content, not the window above it. It's much easier to get if you ever used any new touchscreen devices.
And the old way is wrong—the viewport never moves as we scroll so we were always moving content. Just get used to inverted scheme.
> Granted, it is odd that it's the opposite way round on the iPhone which I use almost as much as my laptop. Go figure!
It's pretty simple: on a touchscreen you're moving the application itself. So having the application "stick" to your finger makes intuitive sense, that's like moving a sheet of paper on a desk, behind a stencil.
On a laptop, you're not really moving the application itself, it's closer to moving a remote-controlled window in front of the application, so moving "up" will move the "window" upwards, and show you what's above the current stuff in the process.
I think about it as using my finger to drag the screen up or down on the mousewheel (like I'm scratching the page down or up with my fingernail). After about a week it is very disconcerting to do the opposite.
I did also need to setup my windows computer to do the opposite direction on scroll though to make the transition work (autohotkey script is on this page).