Start your machine, fire up Spotlight's own window and you can whenever you need to open a file, you get Spotlight to find it. There's o need to know where you saved it last time, no need to navigate through folder hierarchies - it's just there.
As an aside, I should point out that I'm sufficiently anal to have a folder hierarchy, with documents filed accordingly. By and large, I know where files are going to be, so Spotlight, for me, is so far of relatively little direct use. Contrast that with my partner. She saves all her documents in either My Documents - she's a Windows user - or on the desktop. Were she a Mac user, Spotlight would be indispensable. Apple has clearly developed Spotlight not for techies but for all those folks out there who haven't yet learned how to create new folders and drag files into them. Now, we can be smart-arse about their inability to master their machines, but there are rather more of them than there are of us, so ask yourself, who should Apple be catering to first?
But back to Spotlight itself: it's the future. Once all your information is accessible quickly, you won't need a file manager, you just get your data whenever you want it, wherever it is. And it can, potentially, work transparently across networks and network-attached storage. Heck, all it needs is a series of New Document... options, and you wouldn't even need to open your Applications folder. It's almost as if OpenDoc has come back from the grave. I've set Spotlight's not to list Applications and System Preferences panes, but had I done so - as per the default setting - I could launch apps straight from Spotlight. Again, all without opening a single Finder window.
But here's the really interesting part. If you quit Finder - you can add a Quit option by tinkering with the app's preferences file or, more easily, by using Marcel Bresink's useful TinkerTool utility - it stays that way. Previously, Mac OS X would automatically restart Finder. If that's not Apple's way of saying you no longer need Finder, I don't know what is.
What it also can't do yet, is let you copy files to other volumes, of course, even if you've added one to the Dock just for that purpose. So you do need Finder for some things.
Me, I'm in 'old dog != new tricks' mode, so I'll probably stick with Finder for the time being, particularly while Spotlight slowly adds all my less frequently accessed documents to its database. But Spotlight is certainly how I'll be telling new users to find their files.
Spotlight is a major step forward for personal computer data access, and Apple's done it without even having to replace the file system with a database, which is what I expected it to do. Spotlight's own database may become just such a system by proxy, but this way Apple hasn't broken compatibility.