I joined the fabric moratorium thread because I have enough fabric, even if I don't have all the fabric I want.
A lot of it depends on the complexity and size of your quilts. There are plenty of 3-5 yard quilts, but I figure on 10-12 yards for a queen sized project if what I plan on/buy ahead.
If you really really love something, or it's going to be half your quilt: 6 yards -- also big enough for most backs.
If it's going to be a major focus in the quilt: 2-3 yards each of the different colors. I have a lot of 3 yard pieces, I've started combining them in... different... ways to make my backs.
I mostly work scrappy and after working in a fabric shop in my youth I vowed never to buy under 1/2 yard cuts. Half yard cuts may be a little more than a pre-cut fat quarter but not that much.
I have a friend and her method is "if I like it, I buy what's left on the bolt". LOL, sometimes for her that is the full fresh bolt.