has penned a very good introduction to Spotlight
that I recommend everyone read. Spotlight is the big ticket item in Tiger, and for many reasons. My powerbook, Ambrose, is handling Spotlight admirably, though not as lightening fast as Steve's demo machines did (he must be using those Intel based Macs).
He goes over how Spotlight works, how to customize it for your workflow, and even the potential privacy issues that might crop up (here's a hint, open Spotlight and type in 'SSN' or 'Social Security' and see what it finds).