I think it's really important that we do all we can to "sell" our book to the agents--so I think the idea that I already had it professionally edited, had got a well known person (even tho a killer!) contribute, and lined up some experts may have helped.
Not necessarily with regards to the editor. For the most part, it seems agents don't give preference to a ms that's been professionally edited over one that hasn't. A lot of books have been picked up and published that were never professionally edited before being picked up, and I'm sure it's likely that they beat out a few that were. Editing's only half the battle; it's the story you have to tell that agents are more interested in. Obviously we're responsible for presenting a ms that's reasonably free of grammar, spelling and other such mistakes, but professional edits I don't think factor in as much on the decision as you might think they do.