I've only had a few minutes to digest the Leopard preview from today's WWDC conference, but here's one quick observation that jumped out at me. Check out the animation that accompanies the Time Machine's time-based browser:
With Time Machine, you can restore your whole system from any past backups and peruse the past with ease. Can’t find a file you want? Enter Time Machine’s time-based browser to see a snapshot of how your entire system looked on any given day — file by file. When you find the file you want, just select it and restore it.
As far as I know, this is the first mainstream OS to adopt David Gelernter's "lifestreams" metaphor for representing changes in data over time. Essentially, it deals with time the way the physicists did: it makes time a new dimension, extending out "behind" the screen. The normal 2D representation of, say, the contents of a given folder represent its "live," real-time state. When you want to go back in time -- to, say, retrieve a deleted file -- past versions of the folder appear as cards stacked behind the current version that you flip through.
So my first thought was: cool. That's bold. I wonder if Gelernter was involved in some way. I've never been sold on the Lifestreams metaphor as a basic file management metaphor, but for something like Time Machine it seems inspired.
And then my second thought was: what's up with the goofy space image in the background? They can't be serious about that, can they?