I have a porn site as a client, and it would actually be very useful for them.
There are a lot (dozens to hundreds) of generated gallery-style landing pages for affiliates to choose to send traffic to, and having thumbnails of the pages automatically generated would make it much easier for the affiliates to browse through them and pick the ones they want to use.
Out of respect, I'll wait until it doesn't show the latest thumbnails on the homepage before pitching it to my client. :)
I think it was for one of my clients that has a directory service for green service providers in Ontario (http://www.greatgreendirectory.ca/Group/Windfall-Ecology-Cen...). For any sort of directory it would be useful to show the website linked to.