I've thought about it (mostly as my wife is a "fishatarian" won't eat anything with lungs (as someone cleverly coined it earlier in the thread)) but I don't find it appealing for several reasons:
1. meat tastes awesome. I'm a Texan and I'm pretty sure I would wither up and die without BBQ
2. getting enough protein becomes problematic (I lift weights... I'm already taking extra protein on top of the meat I eat, which is a lot)
3. energy density. it takes about 3500 kilocalories a day to maintain my current weight and activity level. eating salads and nuts, that is a ridiculous amount of food. if I can slip a couple pounds of beef in there, it's a lot easier to get enough to eat.
4. there is something primal and incredibly satisfying about eating meat, especially if it's raw or almost raw. if they ever invent a vegetable that tastes as good as raw toro, I'd never eat meat again plus, harvesting a plant is not terribly satisfying either. i don't really get anything out of mowing my lawn, but to kill (and then subsequently eat) a deer or hog is pretty cool. there's just something comforting about eating a rare, bloody steak, feeling the blood run down your jaw, that eating vegetables could never match.

those of you that are vegetarians, how did you overcome these obstacles? I'm stumped.