If you subscribe to The Quilt Show, the latest episode with Laura Nownes demonstrates this exact piecing technique. Basically you sew to within but NEVER past 1/4 inch of where two pieces meet. I am sure there are tutorials on YouTube for sewing Y-seams. It is not difficult but you do have to be precise!
Just found this on YouTube and it is different from the way I was taught but looks even easier!
http://www.youtube.com/watch?v=XLkHfcuNzCA