The panel defined the editing process as substantive edits (changes in plot, setting, pacing, etc.), line edits (less drastic changes, such as in word usage), and copy-editing. The copy-editing stage was done last, to impose a house style and ensure logic and consistency in the story. The final QA step is proofing, which is not really editing at all.
All the writers agreed that only a bad or indifferent editor is the writer's enemy. An important extra step that is often needed is fact checking, and all the writers agreed that an author should find out whether or not his publisher has hired anyone to check the facts in the story.
It was interesting to note that because their books were all from different houses, the writers reported some differences in how publishers' editing cycles worked. Dave Williams' second book, The Burning Skies is from Bantam Spectra, Josh Palmatier's Throne of Amenkor series is with DAW, Jeri Smith-Ready's latest paranormal romance/fantasy Bad to the Bone is from Pocket Books (Simon & Schuster). Because DAW is a much smaller house than the others, the editor is also the copyeditor. Interestingly, she still edited in stages, almost as if she were two people.
It was a fun panel, and very informative. After you have been to a dozen or so conventions, the panels begin to run together but this one stood out.