Being a first-time mom is tough. It's hard not to compare your child to others. My kids were both chunky - I was constantly worried that they were consuming too much milk/formula and both were always above the 90% on weight (thank goodness, they were matched on the chart on height). I'd ask the pediatrician at each visit, and he'd reassure me the kids were fine.
I'm not a "by the book" kind of mom. I prefer to use my instincts. To each his own. But, I needed the book for a few weeks after my son was born and learned what worked for us based upon my interaction with our pediatrician, family and friends.
My only caution with parenting books is that they're out of date as soon as they're printed.
The American Academy of Pediatrics is always updating their policies regarding everything from what your kids can eat (for instance, peanut butter doesn't need to be withheld until age 2 anymore), to how to discipline, to major/minor illnesses. They have a new parenting website that I love and often refer people on this site to: HealthyChildren.org
Because they update the site in accordance with their policies, it's always up to date.
I'm very cautious to refer to sites such as Dr. Sears, Dr. Greene, etc. because the sites are not only written by staff members, but the pediatricians, themselves, can't be practicing much and developing popular website content. Something has to give.
Trust your pediatrician's guidance - especially if they have kids similar in age to yours. We struck gold with ours. But, we don't follow his advice on everything and do a lot of research on our own. We don't agree with his approaches to discipline in all situations, so we do what feels best to us.
We're all opinionated, and it's hard to not compare/judge sometimes.
What your friend is doing is a little invasive and is very much the pot calling the kettle black.
Parenting is very much a learning experience, and our only goal is that we get it "right" more often than we get it "wrong".
Good luck.
Another DanaW