I'm having this debate right now in usenet. I contend that if one drops his or her daily caloric intake greater than 500 cals/day below maintenance (either by increasing cardio, or by decreasing food intake), they run the "risk" of losing muscle mass (assuming that you are not using AS). The greater the defecit, the greater the risk.
I do realize that these losses can be minimized with proper nutrition and training among other individual variables, but in general terms, with little or no experience in training, muscle loss is possible.
I would like to link the results and your reponses of this thread to the usenet group. Besides offering opinions and knowledge, the link may even drive some readers to these boards which IMHO offers a great body of knowledge and training from a great bunch of people.