When the seams are folded to the right and left. Do you machine sew them down? Wouldn't this make them more secure. How about doing a double stitch when the blocks are sewn together?

good instructions with pictures

http://npnt.wordpress.com/putting-it-together-tutorial/

No it dosnt make them more secure because you still only have the one seam holding the blocks togather. The two seams you sew down on each side are only sewn to the blocks. They are not holding the blocks togather. Hard to explain. You have fabric from the backing that you bring up between the two facing blocks and then you sew togather with your zipper foot, this holds the two blocks togather.
Then you fold the backing to each side of the two blocks and sew a seam on top of the blocks. This makes the sashing.
It is simple to do the Fun and Done way since you are not adding fabric to join the blocks, you are useing the backing and bringing it to the front to form the sashing.

To Gail Mitchell - That Emily's Rose Quilt on your blog spot, it is so beautiful, where did you get the pattern from please, I would love to make that one. You have done a beatufiul job with it, wow!!!!!!!!!It is stunning!

From the instructions that I observed in attaching them, you actually will have not only the center seam holding the quilt together but also the sashing strips are sewn to both side of the quilt which should give it extra strength.

I'm pushing this up so I can find it when I get home. I want to save this on my home computer.