Also used as an economical alternative to silk. In addition to the ditch work and applique QuiltE mentions, it is great for tight fill work when FMQ either on domestic or longarm. You can do really intense fill work without all the thread buildup being noticeable. For ditch work it is a dream. It is not as fussy as monofiliments can be.

Here is an example of quilting done with invisifil. Basically you see just the texture left from the quilting, not the thread.
[ATTACH=CONFIG]581448[/ATTACH]

How is the durability of this thread?

I have never had it shred or break while sewing with it. It is a polyester and quite strong. The above pictured quilt was going through batik, an old wool army blanket a layer of polyfil batting and cotton backing. It performed beautifully. I believe I had Glide 60wt in the bobbin on this piece.

Here is a link to an online review of the product
http://www.thequiltjournal.com/review-invisafil-thread/

What needle do you use with it? (I'm using my DSM.) Watson