Spotlight also has keywords -

kind:pdf

date:yesterday

author:short_name

from:contact_name

And the boolean relations AND, OR, NOT work as you might expect.

There's a lot of cool stuff hidden in Spotlight. Try

    man mdfind 

to play around with command-line Spotlight.

Here is a particularly good resource on this aspect of Spotlight:

http://hints.macworld.com/dlfiles/spotlight_cmds.txt

I know you didn't claim Apple invented it, but I thought it would be informative to say Apple have added their own ideas but the main idea comes from BeOS, a once commercially viable operating system. These days it lives on in an open source recreation that has improved on BeOS, called Haiku. It uses a 64-bit journaling file system which has been improved now called HaikuFS that can hold 80,000 petabytes, caches so is fast and has user-definable attributes, like for contacts, music or anything you can think of really which can help you find things fast. There's a reimplementation of Dashboard called Corkboard written by a fan so it goes both ways - good ideas are used elsewhere. :)

Forgot about the dictionary, I use it all the time in spotlight