Thumbnails
They are not bad, but I really like the white background.
One more tip. To use the thumbnails that can be clicked on for full size, go to the Additional Options box under the message box (or click on the paperclip icon on the top toolbar) and click on "Manage Attachments". Then browse out to the image file you want to upload, then click "upload".
This will put the thumbnail at the bottom of the message. When you Preview Post, you'll see it there, and it will open up for you on a white background. But when you Submit Reply and look at it, it will be on a black background with box.
You can also check out the "Test" forum and see how other people have experimented with the photo options.