I ran into an interesting issue where for the first time in a while, Spotlight wasn't finding what I knew existed within my emails. Each time I have to do expense reports (which I just LOVE doing!), I rely on Spotlight search to find my specific airfare, rental car, and hotel receipts that are sent to me via pdf within email messages.
After some googling, I found a method that did the trick:
Enter the following in Terminal:
sudo mdutil -E /
You'll be prompted for your passord and then the index rebuilding process will begin.
After the reindexing was complete, everything worked perfectly. Thanks Hoffman Labs!
Onyx is a great free app that helps in several ways (including rebuilding indexes).