I just posted this on another topic:
It's a matter of preference how you do the borders. If you have a rectangle shaped quilt and you do the long sides first, then the top/bottom, it's supposed to take less yardage of fabric if you are cutting the fabric lengthwise. If I have enough, that's how I cut it myself. Piecing the borders is acceptable too, but some fabrics hide the seams better than others. If I've got more than one border, I do them all the same way.
Edit: here's a helpful site:
http://www.quiltville.com/borderhints.shtml