I've got this lens. I always carry it around for fun stuff. Its not the worlds sharpest lens, but you get 180 degree coverage. Its not rectilinear either, which means you won't get clean straight lines but curves everywhere.
There's a filter for photoshop called "Imadio fisheye" which is designed with this lens specifically in mind. I bought it a week after i received my lens, and I use it to correct almost every shot. Works extremely well, better than photoshops own correction, which cuts out the edges of images. Check it out. Its a brilliant addition.