@sali19,
I had just shy of 8 lbs for my first baby and gained the minimum that my doctor suggested - 25 pounds. The second baby was 8 and half and I gained about 30 pounds.
My doctor didn't hound me about gaining weight - but wanted to make sure I was consistently gaining. Just remember the weight gain isn't simply the weight of the baby, but the placenta, fluid and other stuff. In both cases, I did lose close to all, if not all after having my babies.
Gaining weight is for both your health and the baby's. Depending on what the baby needs - the baby will sometimes end up taking those nutrients from you and thus your health could suffer.