Two key numbers.... the width of the board is the diameter of the largest glass. The builder in our house used 5 inch boards, and none of the glasses are close to 5 inches in diameter, so we have a ton of wasted space. If I were redoing it, I would use 4 inch boards - if there are a few glasses at or larger than 4 inches, just put narrow glasses in alternate rows.
The other key number is the space between the boards. The builder did 2 inches at our house, and I hate to admit the number of glasses I broke trying to make them stay in a rack with a 2 inch slot. I have since put in fillers (ugly), leaving a 1 inch gap, and all glasses fit, and none have fallen through.
I occasionally do work (doors and columns) for someone who builds wine cellars. The "standard" is a sloping cut done on the table saw, but I have done some for him using a panel raising cutter, which looks a lot nicer. Scary though, since you are cutting 40% or more off of each side of the board.