For those of you who wean at 3 weeks, have you noticed any ill effects? I have always waited until 5 to give them the best start possible.
Not at all, I think it's harder on the mother to have any past 4 weeks with her. , the mom will wean them regardless, but it does take the toll on the mother, and they do fine weaned at 3 weeks for me.

If you watch them, the rats will begin to eat the hard food around 3 weeks of age. So technically, I wean at 3 1/2 weeks because I do tub changes on saturday's, and they are most often born on a wednesday.