In the case of fresh water conversion a lot of freshwater fish and plant life is going to take a serious blow (most freshwater fish species will simply go extinct). And probably a lot of people will die of thirst around the world before enough emergency desalinators can be rigged up (do glaciers also go briny? We could see a bit of flooding from all that suddenly-melting ice). But fresh new rain will flush the brine out over time and the ecology will eventually recover. Whereas if the entire oceans of the world turned to vomit it'd take a long, long time to get purified. There will probably be far worse ecological consequences.

This sounds like a serious problem. On the one side, vomit-world. On the other, world hunger would end, but I'd get sick of Veal after a day or two.