Since vegetarianism tends to attract a certain sort of person anecdotal evidence regarding them is shaky at best. It would be interesting to see various studies but I'm not sure there are many I trust since they tend to get hijacked to serve a political or moral point. If soylent (or some future product) does prove successful I would think a lot of vegetarians (as well as meat eaters) would benefit from having some occasionally just to make sure they're getting all their required nutrients.