I use Bobbinfil in all my sewing projects now. It is finer than normal sewing thread and therefore so much more fits on your bobbin. This means changing bobbins less often - which is fab for the impatient sewer! You also get so much more on a standard size reel (1500 metres) and so it is more cost effective too!
It is great for all sewing projects but vital if you are doing machine embroidery as it keeps the tension just how you need it for great results. Give it a try - you wont go back!