Yes, TIME MACHINE. 

Go and click the above link, see the movie, cry with delirium, finish touching yourself, and *then* come back here.  Trust me, it's worth it (well, maybe not the touching yourself part, but I'm not here to judge you).  Install Quicktime if you have to - it's *also* worth it just to get a
GLIMPSE!
OF!
GREATNESS. 

For those of you who just can't be bothered, I have linked a Youtube video below.



Taking the concept of version control and applying it across the entire file system is *brilliant*.  But imagine taking the concept of version control, applying it across the entire file system, *and*:

• making that concept easy for the average end user to understand
• making file recovery look like it's straight out of a Hollywood interpretation of computers

This isn't just sexy to the power of 2, or 3, or 1000 - no, this is actually so hot as to be in its own *dimension* of seductive.  I am warning you, do not demonstrate this feature to a member of the opposite sex unless you want all of your clothes RIPPED CLEAN OFF. 

Mac OS X Leopard may be many other things, but one thing you can be sure of is that it is GUARANTEED ACTION.  And really, what more do you want from an operating system?