Mac OS 10.4 (Tiger) has the neat Spotlight feature which allows you to find all sorts of files very quickly and easily. It even allows you to search the contents of many files, including e-mail messages, pdf documents and Microsoft office documents. There is one flaw however. To do this it creates a database, which it updates periodically. That is all fine and dandy. But if you use an external hard drive from time to time, say for backups, it will also try to index this volume. Not only can this take a long time to index, but you probably don’t want it to return results from that hard drive anyways. The solution – Spotless. It is shareware, with the only drawback for the free version being that you have to wait for 15 seconds for it to start. It is a very simple GUI which lets you set the indexing status for different volumes.
The same problem exists for the unix command locate. Even if you don’t use the locate command, it might be a good idea to follow the instructions in this article from macosxhints