Occasionally I need to search all the files on my computer for a specific word or phrase. The "occasionally" part of that sentence is actually the most important, because it means I don't want to use a search feature that creates and maintains a full index of my hard disk. It takes up space, and slows down my computer. I'd much rather take the speed hit, and have something that can search without an index. I don't search very often, so I don't mind if the operation takes a couple of minutes each time.
For this reason, I don't use the Windows built-in search facility, or programs such as Google Desktop. Instead, one useful recent discovery is a free (for personal use) utility called UltraFileSearch. You can download it at http://www.ultrafilesearch.com/index.html.