I usually buy 2 yards, but if it's a neutral or something I really like and it's also on sale, I buy what's on the bolt.
Glad this question came up. From the 24th to 27th I'll be in Lancaster, PA for the quilt show and fabric shopping. My sister is a new quilter and asked me to pick up some fabrics for her. It's difficult to buy for someone else when they don't have specific pattern, fabrics and yardage in mind, but after reading the responses I'm buying 3 yards per fabric. May in Jersey