Tiger Bits: Boolean Search with Spotlight
Mac OS X Hints has a post today about how to do a boolean (not, or) search using Spotlight. Basically, all you have to do is type a | (SHIFT + \) between any two terms you want to connect with or. If you want to exclude certain matches from a search you just have to add the removed term in parenthesis and with a minus sign.
For example, a search for every document on your computer mentioning Apple or Jobs but without mentioning the iPod would be phrased:
apple|jobs(-ipod)
Pretty nifty. Make sure you check out the comments to this article for more detailed information on how well (or not) this works.