Here's something I just thought about. As everyone has recommended, my goal is to put (2) 120mm fans in the cabinet, probably on opposite sides. The cabinet is 15" wide x 29" high x 24" deep and is constructed primarily out particle board. The particle board is approximately 3/8" thick. The cabinet front and doors are solid maple. There is another 15" cabinet on the right, which completes the support mechanism for the counter, which is solid granite and weighs about 150 lbs.
Will drilling two 120mm holes in both sides of the left cabinet weaken it to the point that it becomes structurally unsound?