Okay, so Spotlight actually debuted back in Tiger. But if you'll give it a try, I'll think you'll find that the Leopard version to be an entirely different animal...
(Sorry, but I just couldn't resist.)
In Tiger, Spotlight was slow, awkward, and in some cases didn't even succeed at its main job of finding files.
In Leopard, Spotlight is now a fast, lean, mean, file-finding machine. Plus a lot more.
As in Tiger, doing a Command-Space activates the familiar Spotlight search bar. But that's where many of the similarities end. So, right now, do a Command-Space, then type the word "disk".
The results are in...
Almost instantaneously, you'll get a result much like the one to the right.
Note that top hit, and the current selection, is "Disk Utility". If the search word is all or part of an application name, Spotlight will usually make it the top hit. Hit return, and Spotlight will run the application.
Do Command-Space, and type "itu" and then hit return, and Spotlight will launch iTunes. In other words, speedy little Spotlight now makes a darn fine application launcher. Goodbye Quicksilver.
Also note that the item just beneath Disk Utility is a dictionary definition. Need to lookup a word? Do Command-Space, type the word, and hit down-arrow and return. Spotlight launches Dictionary and opens it just to the right spot.
The third group lists any of the relevant System Preference panes that may apply. Click and you're there. Bye-bye FruitMenu.
The rest is a well-ordered and extremely clean list of relevant search results.
Spotlight also knows math. Type Command-Space and then "2+2", and Spotlight will give you the answer. For me, that just eliminated a Dashboard widget.
If you know your search is going to be more complex or generate a lot of results, do Command-Option-Space to bring up Spotlight in a Finder search window. Fortunately for one and all, Spotlight in Leopard dropped it's clunky custom interface for one that we all know how to use.
Refining your search...
The new Spotlight lets you refine your search using additional criteria entered via the Finder window. Just click the "+" button near the search box and select the attribute you need. Select "other", and you'll be presented with a list of even more options, including "System Files", which lets Spotlight search every niche and cranny of your system.
Option-click "+", and you can do boolean "and" "or" or "not" searches as well.
In the sample below, you'll see that I refined the "disk" search so that I'm only looking at documents opened within the last three days.

Do this sort of thing often? Click "Save", and Spotlight will add your Search to the Finder's sidebar under the "Search For" section, right along with the "Today" and "Yesterday" smart searches. (Which are really just predefined Spotlight searches.)
More options...
You can even find those pesky invisible files if need be. And speaking of which, if you need privacy, or need to restrict access to confidential information, Spotlight maintains the ability to exclude specified folders and drives. Just go to the Spotlight System Preference pane (using Command-Space "spotlight", of course).
Spotlight will even let you search other Macs on your network on which you have access, which makes finding files on another machine or shared server a piece of cake.
All in all, the new Spotlight is solid proof that Apple listens to its customers, knows when to go back to the drawing board, and excels in refining it's products. But we all knew that, right?
So take the new Spotlight out for a spin. Who knows? It may just redefine how you use your Mac.
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