I am on the side of late-introduction of solids. I wait until 8 or 9 months even to just introduce the idea. It doesn't delay the intro of table foods for us. It just shortens the period of pureed foods, which rocks.
Cereal is full of poor calories. Breastmilk is actually higher in calories per ounce than formula or any solid food out there. There is growing support for exclusively breastfeeding for a year or so.
Good luck finding a pediatrician to support that, though. I've seen a half-dozen pediatricians in my tenure as a mom. All of them suggest solids at 4 months and push them by 6 months, even though my babies are all fat for age.