Here is what I have found out on my journey so far. I am 5'10" was 180 lbs and am 38 years old. I have lifted for years, but never gotten much results. In October I began the Westside for skinny bastards program and began eating 3500 calories a day. Within four weeks I had gained 8 pounds, but most of it was fat, since my waist had expanded more than 2". I then cut back to 3000 calories, but continued to gain fat and grew out of all my pants since my waist was still expanding. I then cut back to 2200 calories. In the last four weeks, since going down to 2200 calories I have gained an additional 4 lbs while my waist has shrunk. My neck, chest, shoulders, arms, and thighs have all gotten bigger. All of my lifts have been steadily progressing as well.
To sum it up: Everyone has said, "Eat, eat, eat." But for me I found that 2200 calories is what works. Listen to knowledgeable advice, but adjust as needed.