Art departments making the move to InDesign from QuarkXPress or PageMaker probably have hundreds, if not thousands of vector EPS files lying around — logos, illustrations, clip art, posters, etc. InDesign can import EPS files, but sometimes the low-res preview that's included with the EPS causes problems with output.
A little tech background for newbies: When you're working in a PostScript-based drawing program like Adobe Illustrator and Macromedia Freehand, saving a version of the drawing in EPS format (instead of or in addition to the program's native format) is necessary if you want to import that image into other program's files like QuarkXPress, Pagemaker, and Microsoft Word. These programs understand that they should use the low-res screen preview of the file (included by default with a vector EPS) to show you what it looks like onscreen, but when the job is output, they should send the underlying PostScript code.
QuarkXPress 6.x users, have you noticed that its optional OPI XTension is installed and turned on by default? If you're trying to troubleshoot random, bizarre problems with your PDFs or printouts, this could be the culprit.
The OPI XT is only needed if you're a worker bee in an OPI workflow, the kind where you're using low-res images in your layouts (for speed's sake), while their high-res versions are automatically substituted when you output to print or PDF or do a Collect for Output . A big fat OPI image server and OPI software on your network runs the whole shebang. It's not really that common these days except for large publishers with lots of huge images.