In my last entry I mentioned that when you mount a shared iPhoto 4 library, you can't copy full images but rather thumbnails.
As it turns out, this is only partly true.
It's true if, in the Organize section of iPhoto, your images are scaled small. Drag one of these images to the Desktop and you do indeed copy a thumbnail.
It's not true, however, if you either scale the image all the way up in the Organize section or double-click it to open it in the Edit section and then drag it to the Desktop. When you drag one of these images to the Desktop, the full image is copied.
You can tell whether you're going to copy a thumbnail or full image by looking at the information area for the photo. If it reads 0 bytes, you'll copy a thumbnail. A larger number indicates a full image.