There are a few advanced settings here and there, but what comes out of your camera and what comes out of photoshop is guaranteed to work with the gallery- all images should, as a matter of fact, unless their EXIF data is damaged. (EXIF is not required, though)
You are right, the EXIF is not required. The last pic I uploaded had no EXIF because it was an HDR and still uploaded just fine. I encode all my Images the same way in JPG with about 90% compression and never have a problem.
There seems to be some weird bug, because the image I uploaded today was the same that did not upload yesterday.