Results are pretty dire, and basically confirm that this works, that lenses work much better, and that I really need to clean my camera's sensor - because of the way they work, pinholes reveal any crud that's there, even if it wouldn't normally affect the image if a lens was used.
I tried some artistic effects which worked quite well - but to be honest, they'd probably work just as well on images from a normal lens. On the whole I think it's an interesting experiment, and I may try to improve on it, but I'm not going to waste a huge amount of time on it. I've reduced the size of the images since they aren't that exciting.
Pinhole lens cap
A couple of typical photos
And some special effects