Yesterday I discovered the joy of tracing coastlines. By chance I found a whole missing island. But on the Osmardender viev it looks as it has been there before. What happend?
You can display deleted ways by using the "U "keyboard shortcut in potlatch… If there is no deleted way then… I don’t know what todo.
Now if you want to have coastlines to trace you are free to trace rivers in the northen parts of Sweden. There’s a huge amount of ground to cover… 
You can also check out EVS islands who makes beautiful island maps of the world.