I thought I was a hardgainer too. When I was 19, I was 135lbs and was lifting six days a week on one of those typical bodybuilding workouts (chest/tris, back/bis, legs, repeat). Sure, I got well defined, and I even gained some strength. But I didn't get very big or that strong. And most of it was my diet. This is what a typical hardgainer considers a lot of food:
Breakfast: Some eggs, toast and juice
Lunch: Turkey sandwich on wheat bread with lettuce and tomato, a piece of fruit and some milk.
Snack: Yogurt, carrot sticks
Dinner: Chicken breast, mashed potatoes and a veggie
Sorry, but that doesn't cut it! And when I started eating more and putting on weight, it was due to two things 1) More calories and 2) Too many carbs!!!
Yep, I ended up eating a lot more food, however, instead of more protein or protein with each meal, I was eating way too many carbs. My plate would be filled with a mound of mashed potatoes, a small chicken breast and some veggies. So when I did gain, I gained a lot of fat.
It wasn't until I really learned more from Berardi's work and reviewing my own food log, that I realized I was eating too many carbs and not enough protein and the right amount of calories to grow.
Once I straightened that out, I made much better progress.
My daily meals always consist of 30-60 grams of protein per meal and my carbs come from fruit, veggies, Surge, yogurt and the occasional low-carb whole-wheat tortilla. No more mounds of mashed potatoes, bread, pasta, rice, etc. However, that stuff is good for "hardgainers" to actually pack some meat and size on their bones.