I said it in the previous thread, but it bears repeating.
I've been a vegetarian (except for the occasional piece of locally caught fresh fish) for almost 20 years. When I'm invited to a meal, I say, "I'd love to come! Since I'm a vegetarian, would you like me to bring a dish to share or should I eat something before hand?" I always get one of three answers:
1) "Don't worry about it! I've got a yummy vegetarian dish for you."
2) "Ooh, I'd love it if you could bring something to share. I was going to grill some steaks: do you have something that might go well with baked potatoes and creamed spinach?" (P.S. My goat cheese stuffed portabellas are amazing)
3) "Hmm, I was planning on my great grandmother's signature 3 meat lasagna with prosciutto as an appetizer and bacon ice cream for dessert. But if you'd still like to come hang out, you're welcome to!"
It gives the host the chance to decide how comfortable they are with a vegetarian guest (and an easy out if the answer is "not at all") and I know that I'm going to have enough to eat, one way or the other.