Haven't actually gotten any advice lately, I guess since this is #3 and I have two really healthy, awesome kids people aren't so moved to say stuff... but I remember a ton from when I was pregnant with my girls, and when they were babies.
My favorite, from my grandma: I got myself a glass of water at her house while I was pregnant, and she starts telling me that I shouldn't be drinking water, it has no nutrients! I should be drinking milk or juice... She was really adamant about it, even after I tried to explain how we all need water to survive and so on. Then, a few months go by and I have my daughter, and we are visiting her again. She starts telling me how I should really give my 1 month old a bottle of water sometimes, because you know, sometimes they aren't "really hungry, they just want something in their stomachs". I said, "But Grandma, water doesn't have any nutrients!" I don't think she ever made the connection, but I've always laughed about it.