(This is not specific to Aperture 3.3, but is a general Aperture post)

We know about Aperture’s ability to export a Project as a Library. We know we can simply drag a Project to the desktop to export it. However, there are some limitations.

It’s not possible to select more than one library at a time and drag them to the desktop. If you want to do this, you’ll need to put the Projects in a Folder and drag that folder to the desktop. These rules apply even if you export by navigating the File menu. No matter how many Projects you have selected, it will only export the top Project.

However by placing the Projects in a Folder first, you can export as big of a collection as you like.