It's not just your girlfriend's computer that will be a problem for you -- it's _any_ other computer.
Personally, I think it was a big mistake for Apple to do this. I find it very un-intuitive. Even if the design of the way windows scroll was ultimately an arbitrary decision, it's ingrained now. I think it was silly to change it.
What's un-intuitive about it? On touchscreen—you move your finger up, content moves up. On Lion—you move your finger up, content moves up. Took me 40 minutes to get used.
Personally, I think it was a big mistake for Apple to do this. I find it very un-intuitive. Even if the design of the way windows scroll was ultimately an arbitrary decision, it's ingrained now. I think it was silly to change it.