I followed a vegan diet for 9 months before going back to vegetarian. Unless I brought food with me, it was tough to find anything to eat. I missed being able to grab a slice of pizza.
For a cheese substitute, I used nutritional yeast, which is a lot better than it sounds.
I agree with Whaler, you can perform well on a vegetarian diet. I used to race bikes (road and mountain) and discovered most of the top athletes never ate red meat. They ate a lot of pasta.