Answer
Prior to Service Pack 1 for ArcGIS 8.1, the Portable Document Format (PDF) was the most easily portable export format available in ArcMap. The PDF format is supported by most common graphics applications, including Adobe Illustrator, Macromedia Freehand, and CorelDRAW.
With the release of Service Pack 1, the Adobe Illustrator Format (AI) is now the most easily portable export format available in ArcMap. The AI format is supported by many common graphics applications, including Adobe Illustrator, Macromedia Freehand, and CorelDRAW.