I did the Quilt in a Day Sues and Sams for an internet swap - I made all the pieces with the lightweight fusible interfacing, turned and fused them, then sewed them all by hand with invisible nylon thread. I'll probably never use that stuff again - I'm using very light grey 50wt Essentials cotton from Connecting Threads and I like it a lot better.
I'm doing more large blocks now - the flowers and centers I've sewn with the fusible interfacing, but the stems and leaves, I'm doing with needleturn applique. I used Elmers Washable School Glue to baste the leaves and stems in place - it washes out when you wash the finished quilt. Not something I have to worry about just yet because I've only got the first block done. :)
You can hardly tell that the interfacing is in there if you use the lightweight stuff. I free-motion sew the fusible to the fabric - much faster than machine-guided sewing and holds perfectly through all the trimming and turning and pressing. :)