I'm another devoted Wonder Under (Pellon 805) user, though not in the same class as Melody Johnson, Laura Wasilowski, and Frieda Anderson. I have hand stitched through multiple layers of it without much trouble at all, though I do use a leather thimble pad.
In addition to being very light, extremely secure, easy to use, inexpensive, and easy to find, it's also the widest fusible on the market (17.25"), can be used for pattern transfer, and is simple to run through an ink-jet printer for multiple copies of the exact same pattern.
Here are some great tips, tricks and techniques from the Dean of Corrections at the Chicago School of Fusing.
http://artfabrik.blogspot.com/p/fusing-tips.html
Two tips learned from personal experience, 1) a used dryer sheet will remove 'rogue' fusible from the sole plate of a warm iron, and 2) cutting fused fabric on the bias will greatly reduce the chances of frayed edges showing up (counter intuitive as it is for us to intentionally cut on the bias).
