Generating Gerber and Excellon Files

So, do I really need to?

This depends on the fab you're using. Some fabs, like OSH Park, will ingest the EAGLE CAD .BRD file directly, and then sort out what to do based on the information contained in there.

It is XML, after all...

If, however, you work with a PCB fab that doesn't accept .BRD files, you'll need to generate specific files and bundle them together to make a package that allows the fab to make your boards.

OSH Park again?

Yeah, they have a pretty detailed online tutorial for generating the required files for automation. In that case, you might also benefit from a Gerber file viewer, which will let you preview the generated files prior to sending them off.

This one has a pretty wretched interface, but it's worked and helped troubleshoot dozens of CAM Processor jobs in EAGLE, so that I knew I wasn't uploading a piece of garbage. Many, if not all, PCB fabs worth working with will provide some level of automation and preview of the what you provide, but if you can preview before you go through the headache of uploading over and over, then it's worth the trouble.

More info later.