Wow, I didn't realize how little the basic interface has changed. I mean, I know there's been no radical changes, but I still didn't expect it to take me nearly as long as it did to tell the difference between a 1-year-old and 6-year-old OS.

Amazing how much they've improved "under-the-hood" while keeping the basic interface the same.

PS. If you can't tell the difference between the two, look at the dock - the only way I could figure it out is spotting the new/changed app icons (Launchpad, iTunes, etc).