I have never joined a gym nor hired a personal trainer. I know that a trainer's job consists of designing an individualized workout program for you, and also encouraging or motivating you to do your best and give more effort than you ever dreamed possible. No doubt some are better than others, but as I understand it that's the basic job description.
I don't have anyone designing a program for me; I have to do that myself. But I do have my own personal motivator, who won't let me quit or slack off. Who, you may ask? Yep, you guessed it--it's little Miss Sarah. I was doing my exercise video this morning. It's one of the Walk Away the Pounds videos (I like to call it Aerobics for Dummies!). One of the movements that the video has you do is side steps. The instructor says you can stand up straight to do the side steps, or you can make it more challenging by bending your knees (kind of like a squat) and side-stepping like that. Well, I was dragging a bit, and elected to do the side steps standing tall. That's when my personal trainer piped up! "No, Mommy! You have to bend your knees!" So thanks to Sarah's, ahem, "encouragement" I had a more challenging workout today than originally planned! :-p