This was first recommended to us by DD1's pediatrician (in 2006), and then again with DD2's pediatrician. DD1 could've waited longer as I see it now as she took forever to adjust to food, but I don't regret starting when we did. DD2 was pretty much ready for it. The first week with the rice cereal was the worst. Since we did oatmeal at the third week she's been eating like gang busters.
We were with a medical group associated with Blue Cross/Blue Sheild with DD1, and Kaiser Permanente with DD2. Kaiser in CA is uber crunchy with EBF (however are also supportive of FF moms) so I was really suprised when the pediatrician suggested solids at 4 mos. as I would've waited until 6 mos. had they told me to.