What are some useful ways to use Automator?
Automator helps you automate (pun intended) repetitive actions without requiring programming knowledge.

The basic building blocks of Automator are Actions. Each Action does a sigle task, that may take an input and produce an output. Automator lets you create a sequence of Actions, called Workflow. If you are familiar with UNIX it's like a UI for pipes.

Here is an Automator Workflow I use a lot, especially for downloading lecture notes in PDF from my professors' sites:



Creating Services is another feature I find useful.

Also, you can combine the power of AppleScript with the simplicity of Automator with the "Run AppleScript" Action.

As an example of both techniques, you can check out this service that opens the source of the current Safari page in TextMate.

If you need more information about Automator check this Mac 101 article.

If you are a developer and want to create new Actions or need more insight into Automator, check out this guide and the Apple's developer documentation.