I have used glass for nearly 25 years - having been directed to it by an old woodworker friend of my dads. It is best to use old, tempered glass (true) but if you have some special curve cuts to use for fairing, new glass cuts easier and lasts about as long. Glass works equally well on both hard and soft woods - but the newer the break/cut the better for hard wood. Just save the "worn" pieces for softwood. If you precoat wood with epoxy, glass does wonders to get the coat skinned down, smooth and ready for the next coat. It allows faster recoating for epoxy, as you can scrape to a smooth finish long before being able to sand. In fact, if you can catch epoxy when it is "green" - as it starts to cure, you will be very pleased with the ability to shave and smooth.

One thing to watch - and that is for small nicks or chips in the edge, as it is like pulling a hacksaw blade over the wood with the teeth down - the nicks will leave little ridges.

And for those worried about cutting your hand - the trick is to use a sharp edge and scrape/draw the glass over the wood with the glass tilted at a slight angle in the direction of the pull. If you are pushing down, you aren't doing it right. Only slight pressure is needed. It takes bit of practice, but once learned, you won't want to go back to paper and dust!