Working on the skerry coast around Frjalshöfn, it just happened that I imported 680.000 nodes into JOSM, spreading on a total edge length of about 4.500 km. This results in 150 nodes per kilometer, which means, one edge is 6 metres long on average. Don't worry, I deleted everything. ;-) (Just for explanation: of course, I didn't draw this by hand. I used the "how to create realistic forsest coverage" method from the wiki and then fractalized the shapes).
For an edgy coast line like a skerry coast, what node distance would be adequate? 20 metres? 50 metres?