on the vegetarian thing - when I was training hard as a vegetarian, I upped my intake of legumes and nuts, not carbs. The carb thing is a huge possible pitfall, but if you keep the carbs "honest," you don't risk any crazy weight gain from carbs. By "honest," I mean close to their natural state - whole-wheat breads that are made locally if you eat bread at all, otherwise, brown rice, steel-cut oatmeal, that kind of thing.
The best thing I've seen and used is a diet that stresses foods that are "one ingredient" foods. No chemicals at all. Fruits, veggies, fish, beans, even meat, but only if it's grass-fed, as well as dishes that are made from one-ingredient foods put together.
Have you ever seen Michael Geary's site the truth about abs? He's got great workouts, a great diet style - and by diet I don't mean the-way-you-eat-for-a-little-while-to-lose-weight. I mean a way of eating for the rest of your life that will go a long way to help maintain the health of your body. I bought his book on line a few years ago, and the workouts are really great and I also get a weekly e-zine about healthy foods and workout ideas.
I think the most important thing regarding diet is to stick to a healthy way of eating all the time. (easier said than done!)
