There are many vegetarian Buddhists here in Taiwan and their food is sadly well-known for being overly greasy (as to add flavor). It doesn't help that the local Buddhists avoid onion and garlic, two staples in non-vegetarian local food. It's considered normal to eat supplements, but that's of course a recent phenomenon.
I'm not saying it's all bad (I'm mostly vegetarian), but the studies are all over the place as with everything in nutrition :)
There are so many varieties of vegetarian diet the term is a little meaningless in terms of understanding nutrition.
I've been vegetarian for about 20 years, I eat a lot of fresh veg, not much fried stuff, not much processed stuff, try and make sure I mix things up and get some protein. Broadly speaking I think I've got a pretty good diet.
But I also know vegetarian's who are massively overweight, eat crap (and too much of it), drink too much and so on.
As a broad group I suspect vegetarian's eat better but I think that's more likely to be linked to the fact that this is a group of people who have thought about what they eat as much as anything inherent in the lack of meat.
And that would be interesting (and I think they do exist - I'm curious about the poster above saying that they show it's not healthy because my understanding is precisely the opposite), just I think that there are other factors you need to control for to really understand it.
I'm not saying it's all bad (I'm mostly vegetarian), but the studies are all over the place as with everything in nutrition :)