Another omnivore here. I don't have the time or inclination to become vego BUT think those that do it well should have a very healthy body and be giving themselves a great chance against many diseases.

Just wanted to add that if you are exercising a lot make sure you are getting enough protein as plant sources are not as efficiently processed as animal sources (which could include milk, eggs and cheese if you choose to eat them).

Also be careful falling back on multivitamins to replace the things not in your diet. This link shows an interview discussing recent findings about some antioxidant supplements (inc beta-carotene, Vit A and Vit E) and links to increased risk of mortality. http://www.abc.net.au/rn/healthreport/stories/2007/1861068.htm
. This guy is talking about Danish research but it supports recent American findings. I've not read this particular interview transcript but read a summary of the American findings just the other day. It seems that until now little research had been done into potential negative effects of taking supplements and really its just been assumed (with the help of multivit producers no doubt) that they are beneficial. My personal view - there is no substitute for real food - if you can't get all the vits and minerals you need from real food (with certain exceptions) then perhaps your diet needs to be rethought vegetarian or otherwise.