What's New About Time Machine
Backing up and restoring files obviously isn't new; innovations frequently improve upon things that arent. As reader John Davis pointed out, James Watt invented the steam engine, but he didn't invent steam, the boiler, fire, or the fact that water expands when heated. In the same respect, Time Machine delivers some very new things.
The first new thing about Time Machine is its simple visualization that makes restoration something users can do themselves. I've run backup services for all kinds of systems; one of the biggest problems for backup system administrators is having to perform restorations for the user.
The interface for restoring files from backup is complex and potentially dangerous, if users don't understand where they are directing their set of restored files.
Users also have to be experts in understanding where their missing data might be. Windows XP exposed backup shadow copies in the Explorer Previous Versions view. That's good for standalone files, but does nothing for users trying to restore data if they don't know where the file is. In the case of restoring contacts or photo albums, the data they are restoring isn't even a file, it's a component of a file.
A user with a backup of their iPhotos wouldn't be ready to go after restoring a copy of their iPhoto Library; they'd still need to parse through the directories looking for what they saved, which versions were newer, and struggle with merging the two.
That's the second entirely new thing Time Machine does: track data for users in a non-file centric model. The demonstrated search through Address Book, using search results, is very much a new and interesting feature. It works like people think, not as system administrators plan. Do Windows users even know that Outlook has stored their personal folder of contacts in:
C:/Documents and Settings/username/Local Settings/Application Data/Microsoft/Outlook/user.pst?
Good luck finding that and restoring it using Volume Shadow Copy: that file path is invisible by default!
A third new feature of Time Machine is that it delivers a system wide service that developers can hook into to optimize backups, so that backups only involve the real information users might want to recover. That is a key new thing: VCS just backs up a volume or set of directories without regard for how much of the data would be useful to actually archive. Developers have no mechanism to tell Windows not to back up their scratch files.