I've been experimenting with "black glass" which is technically a 9 stop neutral density filter. It's not dark on the top and clear on the bottom like a graduated nd would be. This is a round, and very dark tool that can allow you to manipulate the light in some creative ways.
I used it to shoot a 50 second exposure in broad daylight. Normally this would have completely overexposed the scene, but by blocking 9 stops of light, I was able to show the motion of the cattails swaying in the wind.
For the Lighthouse shot, I used a thirty second exposure while the sun was still high in the sky. The camera was tripod mounted to keep everything sharp. Yet, notice the motion of the tall grasses. This is something I would not have been able to achieve without the filter.
I also tried it at the beach to create the dreamy water effect. This was done with a 30 second exposure. Without the filter, the water would have had more definition to it. While that's not necessarily a bad thing, this is an interesting look and technique that definitely has it's place. I'll be experimenting more with this over the next few weeks and will detail my findings here.