I would think it would depend a great deal on what you usually make. I primarily make bed size quilts; and usually king size. I would think about 3 1/2 yards if I thought it would be a border. 1 yard for binding, 2-3 yards for focus fabric, 2 yards for blenders.
If you primarily make wall-hangings, baby quilts, tablerunners, or other small projects, then I would think 1 yard or even fat quarters would be appropriate.