So, how's this for timing!
Author Lisa Shearin has just started posting a series of articles on her blog about the revision process when an agent and editor are involved. She speaks from personal experience, drawing examples from her first novel, Magic Lost, Trouble Found.
Personally, I found it very interesting to see what kind of things an editor will look at changing in your manuscript. If you think it might be interesting, check out the first article here in the March archives.