I have a Janome 6600 and I use decorative stitches all the time for quilting. Some stitches are adjustable. If I'm using a new one I try it out on scraps of cloth-lined batting (try to use the same weights as in the quilt). I always use a walking foot for any quilting.
I just finished 3 lap robes using the star (asterisk) pattern and sewing it in an undulating line the length of the quilt (the cross wise were quilting as I put the top together). I used black thread and several people have commented on them very positively.
I've used several patterns and often use a plain straight stitch also (don't tell the new quilt police who like the squiggle quilting... it's just not my thing). I also use a pattern to sew down my bindings (I have arthritis and no hand sewing for me!).