I've never thought of myself as a T'art," but after considering it, I think I like it.
Yes, I changed over to a Pescetarian diet in the middle of my weight loss. I had already lost 15 lbs, and I lost another 15 after. The diet change was not about the weight loss. Since the end of my diet, I've maintained and lost even a few more lbs.
Additionally, I have decided to adopt a fully vegan diet. This came about from the discovery of fake shrimp. I have no need for real seafood ever again. Veggie sushi has even grown on me. I thought that would be more of a struggle.
My advice for a person trying to lose weight is to increase fiber and water intake. The content of your food and not just the caloric value has, in my opinion, a very dramatic effect.
I think 5 lb/week is a good guideline, but I think that should be calibrated to the person. This was acceptable for me: A 27 year old 5'9" male who started at 195 lbs and could budget three 45 minute workouts a week. This guide probably can move in either direction based on the individual and their activity.