I have used them quite a lot. I have a pad of them next to me as I type this, actually. Personally, I think they're great. They can be used to solve all sorts of maneuvering problems - even very complex ones.
One thing to keep in mind, though, is that you don't really need a pre-printed maneuvering board to do the plotting. It makes it convenient, but you can do the exact same plots with a ruler, compass and a pair of triangles or parallel rule on plain or graph paper. Celestial navigation plotting sheets can also be used.
If you haven't already read it, the
maneuvering board manual (chapter 6) is an excellent resource for learning many of the things you can do.
I can provide you with a link via PM to a high-resolution scan of a maneuvering board if you are interested. I don't want to make it public because I am acquainted with a gentleman that sells the pads and I am also unsure of any copyright issues.
Cheers!