I just finished upgrading our Mac (my wife and I share it) to Lion. It looks very nice. This has been the OS X upgrade to which I have given less thought: purchase, download, backup, install, done.
I think a lot of this has to do with the online distribution. We are used to installing things downloaded from the Internet without much thought (of course there are security considerations, but that's another topic). On the other hand, new OS versions used to be special: you go to the store, or you order it online, it comes in a box, and there used to be an ominous feeling about it. It may wipe all your data, it may make your machine unrecognizable, it may kill your pets.
But when a major OS upgrade comes through from the App Store, it feels just as if you are installing another app. It's much less frightening. And Apple has removed pretty much every question about installation options, which helps this feeling. And it works, which gives you assurance for next time.
All in all, a pleasant, reassuring and painless experience. Well done Apple.
And this reverse-scrolling thing in Lion? I think I'll get used to it pretty quickly. I use my iPhone so much that it almost feels natural on the Mac as well.