I have seen many quilts that had words quilted into them...I think it is an awesome idea!!!
One thing to remember...it may be better to have a backing that the quilting thread does not show up on really well, the words will be backwards there...
One person used thread so it would not really show on the front, but did on the back, because they wanted the more personal message only to be noticeable when it was placed in front of a mirror.....