I freaking love my ergo. My 7 week old son is already 13lbs8oz and the moby worked for all of two weeks for us before he felt too heavy and long for the newborn carries. We use our ergo with the infant insert and do a front carry for now. He is 24" long and can now see over the top of the ergo and the infant carrier and loves to look around while I am fixing dinner or doing laundry. Of course he always falls asleep - one of the best features!
I digress, my question for Ergo users is this: at what point did you remove the infant insert? The box says four months. He is already getting too big for the insert! I like how it provides neck support, but he is already so long that if he keeps growing, the insert won't be providing neck support for much longer. I'm just curious as to why Ergo would pick a seemingly arbitrary number - 4 months - instead of pointing towards weight, height, and developmental milestones...