The issue with 8" distances between quilting lines is that when the batting is wet from being laundered, the weight of it can pull against the quilting lines and cause the stitches to break. That said, since the recipient won't appreciate your gift, does this really matter?

I would do this. Then you will be sure that there aren't any problems later on. Just know you did a great job and that is all that really counts.

I don't pay attention to what the batting mfg says. They don't make quilts. Quilt as much as you believe necessary for look and stability. I believe your quilt needs more than 8 inches apart.

I have quilted even further apart than that and my quilt is still in one piece!

Thank you all for your help. I am going to add another line of quilting inthe middle down the middle of each block and will post a picture when I am done. It is the first large quilt I have done (thanks to my new Juki 2010). I put an extra table in my quilt room to hold the bulk and have missed alot of the 'ditches', but I am getting there. Thanks again!
P.S. It is for my MIL who wanted my hand pieced quilt, so this is my compromise...

I don't make quilts for someone if I know they will not appreciate it. They get purses, crocheted name doilies, or something else I think they WILL like.

I hope your effort and time does have some appreciation much more than my effort years ago. For Mother's Day I made my mother and my MIL each a quillow for their beds, king & full size. Both were white with a machine embroidered large rose of their favorite color on the pocket of each. I spent lots of time on these. I never did see my MIL use hers, and just assumed she had it put away for some reason. Later she had to move from her home in another town to be near her sons. Her home was given to a grandson. My DD rents that house now from the GS. DH and I were there helping DD with yard work two summers ago and I noticed a white mat (I thought) lying in front of one of the storage buildings. I picked it up only to discover that it was the pocket with emb. rose from MIL's quillow, that had been literally "cut off" of the quillow itself, who knows where the rest was. DD's puppy had drug it out of the storage building. I was absolutely furious, so was DH. So like others I would suggest perhaps keeping the quilt for yourself and giving MIL something else, as we all know making any size quilt takes lots of time and effort and should never go unappreciated.

I think you would be fine with the batting suggestions, however, if the quilt has blocks 8 inch square, I would probably just do an "X" through the squares, it's easy and quick, plus you'd be sure that there was enough quilting without overdoing it.

Do the best you can and gift it with a smile. You might be surprised.

I ended up doing wavy lines horizontally and vertically. Glad I didn't do anymore. When we went yesterday to give it to yesterday, she laid it on the bed over the ugliest comforter you have ever seen, she said it looked nice then folded it up and said she would use it for summer. (It was about 85 degrees here yesterday). I was so hurt. But my chore is done and she will NEVER get anything homemade from me again. Actually, it is my husband's mother, so he can pick out any cards, gifts from now on. I might add that I did it because she had sights on the quilt that took me a few years of hand piecing and there was no way i heck she was getting that one. Thanks for all the help.