Yeah, I do. I storyboard and script at the same time - I find it really hard to write a comic-script in words only. I need to see what the page will look like to know how much dialogue will fit and so on.
I do all of my storyboards in thumbnail-size, as panel layouts are something I struggle with, and it's much easier for me to get through it if I draw in a small size - that way, erasing and changing my mind about panel-order and stuff is much faster and easier. And when I say thumbnail-sized, I mean it - none of these are larger than the length of my thumb:
As you can see, I write notes to myself in the margins, as well as summaries of the dialogue below each page so that I can remember what everything is and what everyone says. These are storyboards for a Christmas-calendar comic I made last year, and the first page (second one from the left in the top row) turned out looking like this in the end: