I have used Steam-a-Seam and really liked it -- no problems at all. One thing I liked about it is that the appliques were softer than with Wonder Under.
For those who are unfamiliar with it, SAS is a double-sided fusible that is re-positionable (sort of like Post-It notes). It doesn't create a permanent fuse until you iron it down.
Regarding the problem with the applique being backwards, here is one thought I have. With a two-sided fusible like this, there are two sides to the paper. I'm wondering if you traced on one side and then fused the *other* side to the fabric. With a one-sided fusible, there is only one side you can trace on and one side you fuse to the fabric. Not sure, but that's my guess.
I have heard that all of the fusibles can dry out over time, but it's possible to re-hydrate them. Don't know the details of how others have done this, but I would probably pile the individual sheets in a plastic bins and place a damp sponge in there, then seal with a cover and let sit for a week or so.