I haven't done it because of animal rights (I'm ok with eating animals, but not a fan of the mass farming practices... the farms where I grew up all raised their animals humanely [it never really occurred to me that there was any OTHER way to raise cows than to let them out to pasture and to bring them into their nice cozy-but-not-too-small stalls when it's cold or rainy], as well as my dad hunted and fished [always stressing to do it in a way that creates as little distress and suffering for the animal as possible] to supplement what we bought from the store) but more for sustainable reasons (it's far more environmentally friendly to raise plants than animals… there's more harmful gas caused by cow farts than by the entire food shipping industry, not to mention the amount of acreage it takes to raise animals could raise way more food if it was growing plants for humans to eat) as well as the excuse to eat tasty, tasty (hopefully healthy, but not always) vegetarian and/or vegan food 1x a week. I've found that I eat less meat on my omnivore days now as well, as I've realized that eating meat doesn't have to be a default... I only have to eat it on the days I'm hungry for it. And about half the time, I'm not hungry for beef, chicken, pork, fish, seafood, fowl, venison, lamb, goat, or veal. (And, yes, I enjoy all of those at some point or another. Mmm…goat curry.) So I eat vegetarian. I've also realized that there's a whole wealth of delicious vegetarian recipes & cooking (including all sorts of interesting vegetables, fruits and grains) available that omnivores never see or eat. (When was the last time you've seen a recipe with both meat and quinoa?)
However, I'm still not quite good at figuring out how to make sure I'm getting enough protein & other nutrients on my vegetarian days. If I don't eat meat enough days in a row, I always find myself craving it for a few days. I need to figure out how to make sure I'm still getting the vitamins and nutrients I need on the days my protein is coming from non-meat sources. (Fortified soymilk seems to help. Mmm… soymilk.) Also, what's up with the vegetarian options on restaurant menus often times being superhealthy? Not everyone who's eating vegetarian wants the "diet" option... sometimes you want fries with that veggie burger. Also, not all meatless burgers are created equal. I know a place that has a nut-based burger that's AMAZING with blue cheese on it. Also, Lick's Nature Burgers are great.
It's also been interesting keeping a food-based discipline. I've had Monday meals in environments that weren't set up for vegetarians (I just passed on the bacon at breakfast, even though it looked terribly tasty), I've had Monday meals at other people's houses (some asked me ahead of time if I had special dietary needs and accommodated my Monday vegetarianism, others did not [I had to make my own bean salad at my parents' house... oh well]) I've had Monday meals at a funeral wake (you'd be surprised what people sneak meat into), I've had Monday meals on an airplane (I think the vegetarian option I got was better than the meat option), I've had Thanksgiving on a Monday (Canadian Thanksgiving is always on a Monday) & made a vegetarian feast, complete with a stuffed Tofurky with the best gravy I've ever had. It's been an interesting journey.