Thanks much for the feedback! I had actually been using a different method I found on the site for roughing up the coastlines, but repeated use of the Crystallize filter has produced wonderful results. After a little policing to make sure certain features remained intact, I'm left with some delightfully rough coastlines as well as a wealth of small islands just off said coasts. I'm glad I keep copies of layers before applying filters to them.

I have to say, it was quite the welcome surprise to see the creator of the tutorial I'm following be the first to reply.

Now to delve deeper into the tutorial and bring in some color and terrain!